Jacques Maritain Center: Thomistic Institute

Distinguer pour Unir:
Aquinas v. Putnam on the Unity of Nature

John O'Callaghan
University of Portland

In this paper I argue against a recent objection that Hilary Putnam directs at the Aristotelian account of essential or substantial form. The objection is that while the Aristotelian assumes a single essential form for any particular natural kind of thing, the plurality of contemporary sciences shows that there are many essences for any particular natural kind. The setting for this objection comes from within Putnam's worries about how language or the mind "hooks up with the world." Putnam had long argued that no system of representations, mental or linguistic, could have an intrinsic or built-in relationship to the world. To that extent his former objections may be called epistemological, insofar as they were directed at the intentional features of representation in various different accounts. More recently, however, he has granted that the Aristotelian notion of form, and its application to the identity of concepts may avoid the arguments he had deployed over the years. But now he has in mind the Aristotelian thesis that the mind's concepts are formally identical to or the same as the objects in the world that fall under those concepts. The identity of a concept is thus supposed to be determined by some thing in the world with which it is formally identical. He confines himself to the discussion of essential concepts and substantial form, that is, concepts that express the essential characteristics of natural kinds of substances. Consequently, the types of discourse he focuses upon are the scientific discourses within which the Aristotelian presumably thinks the essences of natural kinds are revealed.

When we use a term like 'dog' in our discourse, it succeeds in referring to dogs because the concept we have in mind is in some fashion formally identical to dogs. When we engage in scientific discourse, the concept we have in mind is formally identical to the essence of dogs as determined by their substantial forms. In this audience, this is a familiar picture. But Putnam objects that the various different sciences of today reveal a multitude of essences for any particular natural kind subject to scientific investigation. The application to the Aristotelian account of representation is straightforward. The advance of the sciences has shown us that there are too many substantial forms in any particular kind of thing to provide the unity of conceptual identity required by the Aristotelian account of language and the mind. Since this objection concerns features of the world apart from the intentional features of representation, it marks a shift in Putnam away from what I have called epistemological objections, to a properly metaphysical one. It is, as Putnam himself says, an objection to the metaphysical underpinnings of the Aristotelian account of the mind and its concepts. To put it plainly, Putnam denies, or at least doubts that "substances have a unique essence."

Notice the genre of Putnam's objection. It is a familiar story about the dependence of Aristotle's metaphysics upon the rudimentary state of the natural sciences known to the Greeks. Insofar as modern science has advanced and even replaced the various Aristotelian sciences, it has at the same time undermined and shown Aristotelian metaphysics to be outdated and implausible. And so Putnam has himself written of his own desire to revive Aristotelian commonsense about the world around us, without the "excesses" and "fantasies" of Aristotelian metaphysics.

I will proceed by briefly describing Putnam's argument. My subsequent approach to it will have three parts. First I will point out certain of its presuppositions. Second, I will provide what I take to be my own good but ultimately inadequate response to the argument. Third, I will provide what I take to be a good and adequate response taken directly from St. Thomas.

Putnam's Argument for the Multiplicity of Substantial Forms

Putnam puts forward his argument for the multiplicity of essential forms with an example. Take the several theoretical sciences that may investigate the nature or essence of dogs, for example, evolutionary theory, genetic theory, and anatomy. Each of these discourses will claim to be telling us what is "essential" to being a dog. The evolutionary biologist will say that it consists in a certain history of descent shared by the members of a certain population that is the natural kind, and will discount genetic structure and morphology. The geneticist will say that it consists of a certain genetic structure shared by the members of the set of dogs constitutive of the natural kind, and will discount evolutionary descent and morphology. And the anatomist will say that it consists of a certain morphological structure shared by those dogs, and discount genes and evolutionary descent. It is prima facie manifest that the conceptual contents of these essential descriptions are not identical one to another. To the extent that any particular science, anatomy for instance, does not contain within itself the principles of the other science, genetics for instance, it cannot include genetic information within its essential description. So what counts for it as "essential" excludes elements included by other sciences. One description involves historical events, another genes, and the third bones and the like. But each is supposed in its content to be identical to a substantial form in the world. Consequently, as we have three non-identical essential descriptions of the same natural kind, the natural kind must have at least three types of essence determined by multiple substantial forms, the evolutionary, the genetic, and the morphological. Because they distinguish different essences, it appears that the different scientists must be talking about essentially different things; thus, there is no unique essence to determine the identity of the concept dog, and subsequently to determine the identity of the term 'dog'.

Putnam simply cites the plurality of sciences, but I think it fair and useful to construe his general argument as follows:

Putnam's objection is not unrelated to his problems with different conceptual schemes and what he calls Metaphysical Realism. Putnam objects to Metaphysical Realists that there are no essences "out there" awaiting discovery; instead the conceptual scheme of a particular science determines for itself what counts as essential for it. To be fair, Putnam thinks that once the science has made unto itself an essence in view of some interest of the scientist, everything else falls into place; it's not just anything goes. Still, the distinct conceptual schemes of the distinct sciences determine distinct essences. However, the objection is supposed to be directed at the Aristotelian, and so cannot simply assume this "conceptual scheme" analysis. Putnam reads the diversity of the conceptual contents off of their manifest linguistic difference, terms involving the history of antecedent species, genes, and bones. Consequently the task for the Thomistic-Aristotelian in replying to Putnam's argument is to argue that the prima facie diversity of intensional form does not entail a diversity of extensional form, even as he holds on to the formal identity thesis.

The Presuppositions

I want to begin by considering briefly three presuppositions of Putnams' argument. First, he presupposes that terms like `dog' and 'nature' are used univocally across the diverse sciences that he mentions, or, in other words, that the concepts dog and nature remain the same. He has to do this in order to get the objection going. The objection attempts to drive a wedge between two terms, the subject term and the predicate term of an essential description -- in our example, 'dog' and whatever for a particular science would fill in the predicate space of a definitional statement like 'a dog is essentially ______'. While the subject term retains a certain conceptual identity across the sciences, the predicate term does not.

This identity of subject term is presupposed, since otherwise Putnam's argument is a straightforward fallacy of equivocation. Change the example. Consider these two intances: Jane the geneticist says, "a bat is essentially an animal of such and such genetic structure'," while Jack the manager says, "a bat is essentially a wooden structure of such and such geometric structure." Notice that the essential descriptions are prima facie diverse. But why are none of us troubled in the least by the incipient "argument" between them? Why do none of us worry about whether Jack or Jill will pushed down the metaphysical hill? Simply because 'bat' does not mean the same thing in the two different discourses. It does not have sufficient conceptual identity. Consequently, Putnam is not arguing that substance terms do not have identity conditions, but rather that substantial forms do not constitute those identity conditions.

I wanted to switch to `bats' to bring out and emphasize this point about equivocation with terms that have more obvious equivocal uses in contemporary English. The `dog star' seems mildly anachronistic when many, if not most of us can no longer see the sky through the city lights. But the point stands for the use of `dogs' in Putnam's example, and in general. Will one ever bet on a sea-horse to win, place, or show?

This presupposition remains, whether one is an Aristotelian or a "conceptual schemer." Even if Putnam is right that the conceptual schemes of the different sciences determine for themselves what counts as an essential description, he must recognize the larger discourses within which the sciences take place, and which predetermine the conceptual unity of many of the terms used within the sub-discourses. Indeed Putnam is committed to this unity because he thinks the objection he is posing to the Aristotelian is not an internal Aristotelian objection, but an external one. The plurality of essences position is supposed to be a coalescing consensus coming from outside of Aristotelianism as a fundamental objection to it; Aristotelian natural science is outmoded, and so consequently is Aristotelian metaphysics. He writes that "the greatest difficulty facing someone who wishes to hold an Arisotelian view is that the central intuition behind that view, that is, the intuition that a natural kind has a single determinate form (or "nature" or "essence") has become problematical." There can be no such problem however, if the conceptual identity conditions of the natural kind term is itself conceptually determined within each separate area of discourse. If 'dog' means one thing to the evolutionary theorist, another thing to the geneticist, and a third thing to the anatomist, then they cannot even begin to have the argument Putnam envisages without looking foolish. We are to count many essences of the kind dog, rather than just one. But as Frege pointed out so forcefully, when we count we are not predicating a property of an object, but recognizing instances of a unified concept. There is no counting without some form of identity, represented here in the subject term `dog'.

So the question raised by this first presupposition is what the larger discourse is within which these scientists are arguing, and how it determines the conceptual identity of the terms they take for granted as common.

This brings me to the second presupposition of Putnam's argument, namely, that there are natural kinds. The natural kind terms employed within the disparate sciences refer to sets of objects within the world, sets that presumably have identity conditions. Putnam is not an idealist about things in the world and their features. He writes "not just anything can be called the nature of dogs. On the other hand, it does seem that more than one thing can be called knowing the nature of dogs." What he means by this is that objects in the world have their properties or features. The various combinatorial possibilities of the features will determine different sets within which an object falls. The entire set of possible combinations of features is Wittgensteinian Tractarian form for Putnam, and it is the form that he believes was presupposed to his earlier objections to representationalism. His point would be that no particular subset of this set is in itself privileged over another, as far as we can tell. Thus we are thrown back upon the problem of our interests in pursuing various sciences. Different sciences focus in upon different features of those objects. Once a science has determined for itself what it will focus in upon, from then on the results it achieves are in effect determined by those features, and those features are then "essential" for that science. Consequently, Putnam believes that any claim about the "essence" of some kind of being is interest dependent. In a pragmatic vein, and quoting James, he writes "the trail of the human serpent is over all."

Still he must presuppose that the natural kind with its features is "out there." What is to be counted as essential is interest dependent, but the result of the counting is foreordained by the natural kind and its features once the interest is in place. By analogy think of the candy store. I am interested in how many bags of M&M peanuts I can purchase there, while you are interested in the Bit O' Honey. Once we've sorted out what we are interested in there will be right and wrong answers to the questions, how much does a pound bag of M&M peanuts cost, and do you have enough on hand to meet my desires? If it's the case that the candy store doesn't happen to sell Bun Bars, then if that is your interest, you're out of luck. Nothing you can do or say will make true the statement that Bun Bars are an essential feature of this candy store, just as nothing you can do or say will make true the statement that it is essential to Labrador retrievers that they breath through gills. But the crucial thing for Putnam with regard to those features the candy store or the natural kind does have is that there is no way to find order among the features, no way of arranging or ordering them that is not simply a reflection of our interests in doing so.

Thus the metaphysical key to Putnam's argument consists in driving a wedge between the natural kind and its essence(s), much as at the semantic level the key was to drive a wedge between the subject and predicate in a definition. But driving this wedge is not so easy, as one of his examples unwittingly shows. He asks us to consider the possibility of a "synthetic dog," that is, a dog, not cloned, but synthesized from the appropriate organic chemicals to have, from the point of view of the genetic biologist, the correct DNA. The geneticist is wont to count the being as a member of the natural kind. But Putnam argues that the "evolutionary biologists would not regard a "synthetic" dog as a dog at all. From their point of view, such a thing would simply be an artifact of no interest," since it does not have the history of descent necessary or essential to the population that makes up the natural kind.

Thus even for Putnam, kind membership seems upon reflection to depend upon what the scientists take to be essential to the natural kind, and he cannot so easily drive this wedge between natural kinds and essences. So if the identity of natural kinds is determined solely by extension, upon reflection it appears that short of a larger setting within which the sciences operate, the diverse sciences that Putnam has in mind cannot assume a single natural kind about which they can argue. Here Putnam's Lockean inheritance of real and nominal essences comes to the fore. "We are making unto ourselves the species of things." An essence for Putnam is not an intrinsic principle of being in an object that is studied by the sciences. It is rather an element of discourse. It is part of a classificatory scheme of abstract properties chosen by an interested party. The nominal essence thus chosen constructs the natural kind or species. One is reminded of Quine's memorable statement that meaning is what essence becomes when it is divorced from being and wedded to the word.

If Jack and Jill aren't talking about the same kind of thing when they give their respective accounts of the essence(s) of bats, Putnam's objection is once again based upon a straightforward fallacy of equivocation on `bats'. The plurality of essences is not a problem for anyone, Aristotelian or anti-Aristotelian alike, if one is talking about different kinds of things. Indeed, the Aristotelian expects to find a plurality of essences among a plurality of different kinds of things. The trouble, if there is one, is with a plurality of essences for one kind of thing. There are vexed mereological assumptions involved in questions about the identity conditions of sets, and whether the members of a set are essential to its identity. Short of a mereologist, with the appropriate mandatum, to help us sort through these difficulties, we are still entitled to ask Putnam, if it is neither the members, nor a putative single essence that determines the identity of the natural kind presupposed in his argument, just what does?

The final, and perhaps most difficult presupposition to notice is Putnam's procedure of reading off the identity of the forms involved from the descriptions. We are supposed to be able to tell from simple inspection of the descriptions alone that they are diverse, and that the forms involved, from the Aristotelian point of view, must therefore be diverse. We have difficulty in knowing the natural kind and its features. But our descriptive resources are clear and distinct to us. This prior clarity of our linguistic resources is implicit in Putnam's thesis that it is our interests that are determining what counts as essential for us; I surely know what I want. And it is explicit in the transition from step (2) to step (3) in Putnam's argument. Putnam then makes the transition from step (3) to step (4), from the more and better known to the less, when he argues from the diversity of the descriptions to the diversity of things described, the essential structures of the natural kind.

In this form of argument, Putnam displays his Cartesian inheritance. To be fair, in his work he has wanted to move us past the sort of skeptical questions bequeathed to us by modern epistemology. Still, it can be difficult to avoid something precisely because one is trying so hard to avoid it. Advocates of the linguistic turn in philosophy, Putnam included, objected to the instrospective, and infallible, but particularly the private character of the Cartesian picture of the mind. They countered it with the public character of language. However, it can be argued that the linguistic turn was for many simply a projection of the Cartesian mind into a public and social space. The social mind is as introspectively clear and infallible to us, the linguistic community, as Descartes' mind was to him, the private individual. This is why Putnam's discussion of Aristotelianism is animated by the typically Cartesian question, mutatis mutandis, how it is that language hooks up with the world. He reads the Aristotelian as providing just another failed attempt at answering this question. The question presupposes for its intelligibility an independent purchase upon language apart from the world, just as Descartes' question about the relationship of his ideas to the world required an independent purchase provided to him by his methodical doubt. And just as Descartes had argued from the diversity of his ideas of res cogitans and res extensa to their diversity in res, Putnam is arguing from the diversity of essential descriptions to the diversity of the things described.

A Good But Inadequate Response

My response to Putnam will proceed in reverse order through these presuppositions. Let me begin with my good but inadequate response. The movement from the diversity of our scientific descriptions to a diversity of things described is a straightfoward fallacy. It is not the fallacy of equivocation I have been pointing at thus far. Rather it is the intension/extension fallacy. Consider these two descriptive phrases, 'the morning star' and the 'evening star'. One describes an astronomical body that is typically observed in certain predictable locations in the morning sky. The other describes an astronomical body that is typically observed in certain predictable locations in the evening sky. Notice also that the descriptions are prima facie diverse. Does this diversity of descriptions entail that the evening star is not the morning star? No. In fact, the evening star is the same astronomical body as the morning star, namely, the planet Venus. The fallacy involved in arguing otherwise moves from a diversity of intensional content in descriptions to a diversity of extension, a diversity of objects in the world.

Now Putnam could claim that the example is inappropriate because the terms, and the subsequent judgment, come from within the same conceptual scheme, Astronomy, where his example concerning dogs involves multiple conceptual schemes, Evolutionary Theory, Genetics, and Anatomy. But he really can't avoid the charge in that fashion. In the first place, as a rather famous example taken from the Philosophy of Language of the last hundred years, I am rather confident that not many of those who have used it have been particularly informed about the conceptual scheme of Astronomy in the last hundred years. In the second place, however diverse the sub-disciplines of Evolution, Genetics, and Anatomy may be, they take place within the larger and single conceptual scheme of Biology. In the third place, as I've argued, Putnam's objection requires that the diverse descriptions cannot be understood to be coming from entirely diverse conceptual schemes; otherwise he escapes the Scylla of the intension/extension fallacy only to fall into the Charybdis of equivocation. Finally, and in any case, the objection is not supposed to presuppose a commitment to the "conceptual scheme" view. Thus Putnam has no easy out from this fallacy.

Oddly enough, Putnam is well aware of the fallacy in other contexts, as it plays a large part in the argument of his famous paper "The Meaning of 'Meaning'" That paper is the urr paper in Putnam's argument against the supposed built in, world involving identity of mental representations, and it launched a genre of articles in contemporary analytic philosophy that can be called the Twin Earth Chronicles. The details of that argument are not of immediate concern. What is important is Putnam's recognition of the fallacy, and the ground for recognizing that it is a fallacy. As he puts it there, "the timeworn example of the two terms 'creature with a kidney' and 'creature with a heart' does show that two terms can have the same extension and yet differ in intension." Consequently, one cannot simply argue from the diversity of evolutionary, genetic, and morphological descriptions and definitions that their extensions are diverse.

Now, it is always satisfying in an argument to point out that one's opponent has committed some fallacy, and leave it at that. Still, I think this response, though good is inadequate for a number of reasons. First, it is ad hominem, though not abusive. One feels no need to go on and provide a positive defense of one's own view, until a non- fallacious objection is raised, and Putnam has not done so. But it is damnation with faint praise to be able to say nothing positive of one's view, but only that it has answered all fallacious objections. Second, I think Putnam could make a plausible defense against the charge of committing the fallacy in this case. He may grant that in general it is a fallacy to proceed from a diversity of intension to a diversity of extension. But he might add that it is the Aristotelian commitment to the Conceptual Identity Thesis that avoids the fallacy, and at the same time makes the Aristotelian subject to his objection. By contrast, in the ordinary case of the fallacy there is no claim present that there is an identity between the description and the thing described. It is the diversity of intensions in conjunction with the identity thesis entails the diversity of extensions. That is, after all, the crucial stage of his argument in steps (2), (3), and (4). Consequently, in this special case there is no fallacy involved, and the argument goes through.

I say that Putnam could respond in this fashion, but it would require that he abandon the general force of his argument. His Diversity of Essences Thesis is supposed to be a position coming from outside of Aristotelianism, a position that arises within a coalescing philosophical agreement about the results of modern science. Putnam wants to grant the internal consistency of the Aristotelian account, and defeat it as inadequate to the way things are now agreed upon to be. But adding the identity thesis to avoid the fallacy and defeat the Aristotelian places the objection within Aristotelianism as a matter of consistency. It is no longer the case that the problem is with the Unity of Essence position as such, but rather with the joint satisfiability of the two theses, Unity of Essence and Identity of Concepts. Thus Putnam faces a dilemma. Either his objection comes from outside of Aristotelianism, in which case it is fallacious, or it comes from within Arisotelianism, and it is subject to an Aristotelian response that makes clear what the position is, and why the two theses are consistent.

The Aristotelian side of this dilemma brings me to what I think is the good and adequate response to Putnam's objection, a response shamelessly taken almost whole and entire from Aquinas, mutatis mutandis. First, the argument requires in the transition from (2) to (3) that we be able to read off by simple inspection the diverse identity of the forms involved in the diverse linguistic expressions involved. But this movement from a grasp of the identity of our concepts in linguistic expression to the world, presumably justified by the Conceptual Identity Thesis, is in stark contrast to St. Thomas's Aristotelianism. Commenting on Aristotle's De interpretatione he writes

the intention of Aristotle is not to assign identity of the concept of the soul through a comparison to articulated sound, as namely of one articulated sound there should be one concept;... but he intends to assign the identity of concepts of the soul through a comparison to things.

The first thing to recognize from this passage is that the Aristotelian guided by St. Thomas is not at all interested in the question about how our language manages to hook up with the world, since he can't get the question off the ground. It is a mistake when Thomists try to answer that question, rather than ask how it is that our opponent manages to identify the diversity of his linguistic descriptions. My adequate response will focus upon this contrast of procedure, from things to concept versus from concepts to things.

Putnam could bandage his argument by recognizing that the Thomistic Aristotelian is not going from concepts to things but from things to concepts, and yet still charge that since it is a metaphysical identity thesis, the asymmetry of the epistemological movement does not matter. The diversity of the things themselves, genes, bones, and historical events, must lead to a diversity of essential concepts. Recast the argument as follows:

This possible rescuing of the argument is all well and good, except for the minor problem that it also involves a fallacy. It straightforwardly begs the question in step 4), when it simply asserts the contradictory opposite of what the Aristotelian denies. We've already seen that Putnam cannot argue non-fallaciously for 4) on the basis of the diversity of sciences. For the Aristotelian the diversity of sciences is a result of what are known to be diverse subject matters, not a demonstration of them. Perhaps there is a non-fallacious argument for 4), but Putnam has not given one.

But couldn't Putnam just rest content with common sense, the Aristotelian's own ace in the hole, the commensense he hopes to revise without the fantasies of essentialism? Forget all the rhetoric about the developing and coalescing consensus that the Aristotelian must face. It's that rarest of birds, a metaphysical claim that needs no argument. Bones just aren't the same thing as genes, and neither is identical to historical events. Any fool, including the Aristotelian fool, can tell.

Well, no. In taking this tack, Putnam would be relying upon a vagueness in his initial example, a vagueness to be found in step 4) of the recast argument. Prima facie, it speaks of historical events, genes, and morphology. But no anatomist simply studies bones. No evolutionary biologist simply studies events. And no geneticist simply studies genes. In each case they study kinds, the history of kinds of events, the bones of kinds, and the genes of kinds. Lest one object at this point that it is a disputed question in the Philosophy of Biology whether Biology requires the notion of kinds or species, recall that I pointed out in the second presupposition that it is Putnam's argument that presupposes the unity of a kind that is being argued about. If he gives up that presupposition, we have a different argument on our hands, since Aristotelians expect a multiplicity of essences for a multiplicity of natural kinds. But so long as he holds onto it, the point stands. In Putnam's example the scientists are not studying history, bones, and genes, but the history of dogs, the bones of dogs, and the genes of dogs. Looking back at my outline of his original objection, it turns out that step 2) is false when it claims that the essential descriptions of X's (dogs) given by the different sciences are manifestly diverse. The formal identity and unity of the linguistic expressions involved is to be found in the formal identity and unity of the kind considered in its evolution, genetics, or morphology. The essential unity to be found in a kind may be diverse in the way it is considered, but not in what is considered. That is, incidentally, the point behind the gruesome Aristotelian insight that the anatomist's hand is only called a hand analogously.

It would be well at this point to remember that no Aristotelian thinks that the form of X is read off of X by simple inspection. One comes to understand the form through analysis, and then synthesis. As Maritain put it, "we distinguish in order to unite." If this is true of res extra animam, a fortiori it is true of res in anima, since, as we have seen, the Thomistic Aristotelian identifies the form of expressions in the soul from the form of things beyond the soul. Despite the prima facie appearance of diversity in the expressions provided by the different sciences and their sub-disciplines, in any particular case of a natural kind they are formally identical because they express in different ways what is not diverse in things beyond the soul. Indeed that is what the truth of such expressions consists in, on a Thomistic theory of truth, that what is understood separately or diversely by the mind is predicated to be one in things. The unity of subject and predicate adequately captures the unity of the thing defined, and is thus true. Contrary to Putnam's first presupposition, no wedge is to be driven between subject and predicate, since the unity of subject and predicate in a true proposition is the unity of the being in the world that the proposition is about. But none of this analysis makes sense, if we think that our knowledge of the form of our expressions precedes our knowledge of the form of things. When we engage in the act of defining some scientific object, we are in pursuit of definitions that more and more adequately express the formal unity of the thing defined.

Of course at this point I am subject to the charge of begging the question that I just directed at Putnam. As he simply asserts the essential diversity of a kind, I am simply asserting the essential unity of a kind. We are at a standoff. But, is there no argument for my position? Here I turn for aid and comfort to St. Thomas, though the careful listener will have seen the trail of the Angelic Doctor over all. It was disingenuous of me to claim that my good but inadequate response earlier was my own. It was also shamelessly taken from Aquinas, from precisely the same place where I will now look for the good and adequate response.

While Putnam thinks his objection is new, and a product of reflection upon the advances of modern science, like the words of the song, "everything old is new again." By now most of you will have guessed what I have in mind. The fact is, Aquinas dealt with Putnam's very objection, mutatis mutandis, when he addressed the medieval plurality of forms argument, among other places, in question 76, article 3, of the first part of the Summa. Recall the terms of the debate. The objectors argue that there must be a plurality of substantial forms in a human being because of the diversity of "scientific" descriptions under which a human being falls, vegetative, sentient, and rational. Consider this particular objection that Aquinas cites:

The Philosopher says in Metaph., viii., that the genus is taken from the matter, and the difference from the form. But rational, which is the difference constituting man, is taken from the intellectual soul; while he is called animal by reason of his having a body animated by a sensitive soul as form to matter. Therefore in man the intellectual soul is not essentially the same as the sensitive soul.

Notice that the objection begins with a diversity in how man is "called," rational, or animal, when an essential definition is put forward. The reason given for the diversity of "calling" is the diversity of substantial forms in man. Thus the manifest linguistic duality of the definition rational animal reflects a real duality in the thing defined.

The background for the argument, not surprisingly, presupposes two streams of thought. The Aristotelian stream of the objection is unmistakable from the language of definition, genus, species and difference, as well as the analysis in terms of form and matter. But the other is the Augustinian insight into the great diversity between animate life as we see it in animals, and the rational life we know ourselves to possess when we turn within and reflect upon ourselves. In the De trinitate, Augustine had distinguished the mind, the inner man, as the major part of the soul, and as consisting of memory, intellect, and will. But he had also written of the "outer man" that

anything in our consciousness that we have in common with animals is rightly said to be still part of the outer man. It is not just the body alone that is to be reckoned as the outer man, but the body with its own kind of life attached, which quickens the body's structure and all the senses it is equipped with in order to sense things outside.

Augustine's reference to the principle that "quickens the body's structure and all the senses" is enigmatic, as it is not clear in him whether it should be taken to be a part of the soul, or another soul entirely. It is, after all, the body's "own kind of life attached." But it is clear that Augustine thinks it is to be wholly distinguished from the life of the mind, even if the mind and the quickening principle of the body are two parts of the soul.

Now in his disputed questions on truth, De veritate, Aquinas manages to preserve this special character of mind in the Aristotelian language of powers, when he held that the mind was a special "general power" consisting of the particular powers of memory, intellect, and will. This general power had its own special unity to it, over and above the unity it has in the soul with all the powers of the soul, vegetative and sentient. So Aquinas manages to preserve the special Augustinian emphasis upon the distinctiveness of mind within the Aristotelian emphasis upon powers, the soul, and its union with the body. It is rarely noted, however, that Aquinas abandons this "special" character and unity of the Aristotelian mind in the Summa. No longer are memory, intellect, and will given pride of place as a single general power within the soul; no longer do they have their own unity apart from and mediating their unity with the other powers in the soul; but rather, all of the powers, sensitive, animate, and rational are hierarchically ordered and united in the soul itself.

It is clear that Aquinas' abandonment of the Augustinian mind was driven by the plurality of souls debate, and his greater appropriation of Aristotle's De anima, particularly the line by line commentary that he was writing as he wrote the first part of the Summa. In the De veritate Aquinas was not at all concerned with the plurality of souls discussion. But in the Summa he is. His 13th century Augustinian opponents could very easily use his Aristotelianism against him, and argue that if the mind has the special unity and life that Aquinas grants to it in the De veritate, then it is not sufficient to hold that it is a general power of the soul; it must be another soul entirely. On Aristotelian grounds, a distinctive form of life requires a distinctive principle of life, a distinctive soul. This argument is precisely what is taking place in the objection that Aquinas considers, an Augustinian objection posed in Aristotelian terms. To resist that move and retain the special character of the mind in the soul could only be ad hoc on Aquinas' part; and to his credit he abandons the grounds for the objection.

What concerns me here are the reasons Aquinas' gives for rejecting the plurality of souls. Aquinas' first response is my own inadequate response. Often calling it "the error of the Platonists," he diagnoses in his opponents what I have called the Intension/Extension fallacy, to confuse the features of our manner of knowing with the features of the thing known.

We must not base the diversity of natural things on the various logical notions or intentions which follow from our manner of understanding; for reason can apprehend one and the same thing in various ways.

Notice the generality of the point. It is not simply about the plurality of souls debate confined to human nature. It concerns any movement from the plurality of ways we understand to a plurality of things understood. And just as Putnam's objection was general, though confined to a particular example, we can appreciate the generality of the principles involved in the plurality of souls debate, and how to extend them beyond that particular conflict.

My reason for saying that this is a good but inadequate response is that Aquinas himself treats it that way. Yes indeed, the plurality view is fallacious if it rests merely on the diversity of descriptions involved. But Aquinas recognizes that with an additional thesis no fallacy is involved. He writes, "the opinion [could be] maintained if, as [Plato] held, the soul were united to the body, not as its form, but as its mover." Notice the similarity to Putnam. A fallacy may cease to be a fallacy with the addition of a substantive thesis.

Thus Aquinas turns to offer positive arguments for the unity of the soul, and not simply defenses against the plurality position. He offers three arguments, two of which bear directly on Putnam's objection. The arguments focus upon the formal character of the soul, which Aquinas has just stressed in mentioning the Platonic position as a contrast. The first argument focuses upon the unity of the object under consideration. The metaphysical function of form is to provide the unity of being present in some object. Aquinas writes:

Nothing is simply one except through one form, through which the thing has being; for a thing is a being and is one from the same principle; and so those things which are named from a diversity of forms are not one thing simply, as for example a white man.

St. Thomas asserts that if something is described through a diversity of forms, it is because it is not absolutely one. But notice the difference between saying that and saying, on the other hand, that any diversity of descriptions involves a fundamental diversity of forms; the latter is what St. Thomas flatly denies as fallacious, as the "error of the Platonists." So here he cannot be taking the diversity of descriptions at face value. Rather, the diversity or identity of forms in a description is judged on the basis of a judgment of the diversity or identity of those forms in res extra animam, not vice versa. Consider the examples `a man' and `a white man'. According to his initial good but inadequate response, we cannot simply read off of `a white man' that it involves a plurality of forms in res extra animam. On the contrary, we judge that the description `a white man' involves a diversity of forms because we already presuppose that white is a diverse form from man in res extra animam . Apart from our knowledge of the diversity of white and man in res extra animam, we cannot judge the description `white man' to involve any more forms than does `man' alone, or for that matter `white' alone.

Thus Aquinas argues, "an animal with many souls would not be simply one." But the unity he has in mind here is the unity of the natural kind that Putnam presupposes. He writes explicitly "...in things composed from matter and form, something is one through the form, and derives both its unity and species (natural kind) from it." To recognize a distinctive unity of life amidst diverse acts in a species is to recognize a distinctive form of life for that species-- that this is the life of dogs rather than cats. Thus in the life of a species or natural kind of animal, when we recognize a unity of life, we recognize a unity that cannot be adequately accounted for on the supposition that there are many essences present in the natural kind.

Aquinas' first argument then sets the stage for his second argument that focuses directly upon what is involved in providing an essential definition; as he puts it "from the manner in which one thing is predicated of another." The key contrast is with accidental predication. The example, as might be expected in the context is rational animal. Man is a rational animal. Think of the contrast he has just mentioned with "a white man," or "man is a white animal." Aquinas writes, "those things that are derived from different forms are predicated of one another accidentally." A definition by contrast is true to the extent that its parts, genus and difference, are united by the definition in a way that reflects the simple unity of the form in the thing defined. Thus a man is said to be an animal through some form, a sentient one. Now suppose the man were said to be rational through another form, and vegetative through yet another form. Then the relation of rational life to sensitive life to vegetative life in man would be accidental, no more related one to another than is the relation of being white to being rational or sentient, and so on. On the contrary, man is rational, animal, and vegetable through one and the same form. That is why the definition man is a rational animal is both true and necessary.

It is not as if we have two forms tied together by some metaphysical glue called necessity. We have but one form, and the necessity involved is the necessity of self-identity for forms, that is, the transcendental character of being that Aristotelians including Aquinas call unity. It is impossible for there to be a man who, lacking the form of animality, retains the form of rationality, or lacking the form of rationality retains the form of animality, precisely because it is one and the same form by which a man is an animal and is rational. Recall that the setting of the argument holds that a being is a man through the rational form. So Aquinas writes "it is necessary for something to be an animal and to be a man through the same form; otherwise no man could truly be an animal in such a way that animal could be essentially predicated of the man." The contrapositive is equally true, namely, that no animal could be truly called rational in such a way that rational could be essentially predicated of the animal.

This analysis is confirmed throughout Aristotle's and Aquinas' works. Consider the movement of the De anima from vegetative to sensitive to rational form, as the higher type of form is not joined to the lower by "metaphysical glue," but rather includes the powers of the lower form within its unity. Consider the argument in the Nichomachean Ethics for the superiority of intellectual life to any other form of life. Its superiority is not based upon its being a wholly other form of life than is exhibited in the animal life of a man, but rather because the act of intellect is the ultimate formal character of both the practical life involving the body and the theoretical life that in some fashion does not use a bodily organ. The argument is based upon recognizing in human action that reason does not add something additional on to animate acts that are the same in other animals; it is rather the formal aspect of animate acts in human beings that renders them specifically different from the acts of other animals. When Aquinas in turn argues that the act of intellect does not employ a bodily organ it does not follow that it is not the act of an animal. What follows is that not every act of this animal is the act of a bodily organ. And it is not that this animal who grows, moves, eats, and reproduces also happens to think. It is rather that the form of this animal's growth, movement, eating, and reproduction is rational, or ought to be, given what it is for this animal to be. Its is implies its ought.

Finally, this account is confirmed by Aquinas' analysis of what it is to be rational in question.. Aquinas argues that rational means movement from one thing known to another. But the reason why human beings move from one thing know to another is because their mode of knowing is propositional. Propositions are formed from the partial, inadequate and simple grasp we have of things by means of our intellect. So Aquinas argues that truth is only found in a judgment, since only there do we find an act of intellect that is adequate to its object in asserting that what is understood diversely is one in reality. We then reason in argument when we relate these judgments one to another according to principles of reason. But our intellect has these partial and inadequate grasps of things because of its abstractive character, that is, because of the way in which it engages its object through the sensitive acts of the body. Thus rationality is the distinctive form that intellect takes in an animal. By that account neither angels nor God are rational. It is because the formal principle of intellect in man is the very same form by which he is an animal that he is essentially rational. Consequently, in man being an animal is not adequately understood until it is understood to be rational, and conversely being rational is not adequately understood until it is understood to be animate or incarnate, that is, as the act of a specific animal. It is impossible for either angels or God to be essentially rational precisely because they are not essentially animals. The only regulative ideal of reason that Aristotle and Aquinas would recognize is the good man.

Thus definition brings about an enrichment of the form of the subject by the form of the predicate because subject and predicate are expressions of the same form. Here Aquinas' remarks on the transition from the "vague universal" to the "distinct universal" are appropriate. Putnam thinks of the Concept Identity Thesis along the lines of a synchronic judgment that two trees, for instance, have the same form. Since the linguistic expressions appear different they must not have the same form, just as in observing these two trees we may judge that they do not have the same form. The better analogy is the diachronic recognition that the acorn and the oak are the same being, and have the same form, one rudimentary the other flourishing. Simple observation at any particular moment will not tell us this. Rather, we must attend to the genesis of the one from the other, to recognize that they are really one thing after all, despite the appearance of being one thing and then another thing. Just as one cannot drive a wedge between the acorn and the oak, neither can one drive a wedge between the subject and the predicate in a definition.

Recall that Putnam had granted that "not just anything can be called the nature of a dog." Aquinas' would ask that if Putnam is right about the multiplicity of essences, why not? Applying Putnam's point to Aquinas' example, presumably Putnam does not want to grant such claims as that being white is part of human nature, that is, that the description white man is an essential description of the natural kind, however much racists might want it to be. But why not? Recall that he cannot appeal to the fact white is not a feature of all members of the natural kind. We saw with his example of the synthetic dog that membership in the natural kind depends upon what is taken by the interested party to be essential to the natural kind. The unity of essence position rests, among other things, upon the insight that in man being rational has a lot more to do with movement, reproduction, and eating than does being white; indeed that in man, being rational, mobile, gustatory, and reproductive are fundamentally the same thing, while being white is not.

Notice, when a genetic biologist presupposes that evolutionary descent is not essential to his discourse, he may be engaged in his science. And we could ask whether that presupposition is required by his science. We could argue that he should take account of evolutionary descent, or at least show how his genetics sheds light upon evolution, and so on. But when he begins to respond to these latter concerns, and argues rather than presupposes that evolutionary descent is not essential to a natural kind, he is no longer engaged in his science as such. Presumably it is not a well confirmed hypothesis of any particular natural science under which some being falls that there may be a multiplicity of natures for that being, a multiplicity required by the multiplicity of sciences other than that particular one. What exactly would the experiment be that might falsify or confirm that hypothesis? How does such a hypothesis exhibit within a particular science the theoretical virtues of simplicity, predictive power, and fruitfulness for further research programs? It is clear that such a thesis is not part of any particular science, but is rather an extra-scientific philosophical position that one takes about a science. And it is not simply read off of the descriptions and success of contemporary sciences, as if it were a clear and distinct idea. It requires philosophical argument to show that a multiplicity of essences or natures is a necessary condition for the possibility of some one kind of being falling under a multiplicity of sciences.

Returning to Putnam's objection, is it or is it not the case that the different scientists presuppose a fundamental unity in the natural kind that bears upon the diversity of their essential descriptions? Of course there is. What is the fundamental evidence that the evolutionary biologist points to as supporting his theory? The fossil record, that is, the fossilized remains of the morphology of the species he studies. What is the Holy Grail of geneticists and evolutionary biologists when they get together? We've all seen the fantastic account provided by Steven Spielberg, but it is to find genetic material the structure of which shows how the genetics of life coalesces with the evolutionary chain observed in the fossil record. Does the geneticist think or not that the genetic structures he studies find no differential expression in the morphology of the animals he studies? I am not even an amateur in Biology. My own field of undergraduate study was Physics, and there the examples of unity in diversity are legion. Perhaps the most famous example is the fundamental unity behind the Ideal Gas Law in Chemistry, and Statistical Mechanics applied to Thermodynamics. One "conceptual scheme" trades in molar quantities of elements, while the other trades in the kinetic energy of vast ensembles of atoms and molecules. The random walk phenomena of Brownian motion in Fluid Dynamics and Statistical Mechanics applied to atomic collisions is another example. Black Body Radiation in Thermodynamics and the analysis of the quantum radiation of electromagnetic energy given by Plank and Einstein in the development of Nuclear Physics and Quantum Mechanics. Those who are being educated in the sciences are taught that finding this unity in diversity is a theoretical virtue in the sciences that goes beyond simple experimental confirmation or falsification; it is certainly not a curse. Indeed does anyone really expect the sort of argument that Putnam imagines? What little I know of Biology suggests to me that the scientists in question will greet each others results with excitement to the extent that they confirm their own theories, and dread to the extent that they undermine them. Yes dread, precisely because they know that the results of other sciences do bear upon what they take the nature or essence of their object of study to be. They don't want to engage in a science that is fundamentally different from and possibly even inconsistent with everything else we know about the world. Contrary to the story line of much of the history and philosophy of science in the modern period, we should not be singing dirges, but rather songs of modern science's vindication of Aristotelian metaphysics with its commitment to the unity of nature. Distinguer pour unir.