JMC : The Physical System of St. Thomas / by G.M. Cornoldi, S.J.


IN fact the mixtum or chemical compound is a substance that has properties and operations invariably different from those of the elements of which it is composed: but the principle of activity, or substantial form, is the source of the properties and of the operations. Therefore the substantial form of the elements, which is really distinct from their matter, is different from the substantial form of the mixtum; and so, in that passing from the state of being elements to the state of being a chemical compound, there was a true substantial change. Now what is there to be said against this argument? Can the elements co-operate to the same term of operations, and thus operate in specifically different ways, retaining their own proper principles as before? This cannot be. The operations resulting from co-operation of separate principles must reveal the disposition of these principles, either in an equal degree, or as shewing what more belongs to the stronger. Thus, for instance, if the two elements disjoined attract a substance, together they will attract it more strongly: and if one of them attracts while the other repels, the attraction and repulsion will be according to the difference of their contrary forces. Can it be said that the elements themselves by virtue of their union, not only co-operate to a term of operation, but give besides one sole principle of it? This would suppose the impossibility, that each atom remains in the mixtum as a true individual in its own nature. St. Thomas therefore says:

"It is impossible that of things different in being there should be one operation. I say 'one,' not speaking of the term, but of its proceeding from the operator. For many men pulling a ship do one action as to the thing operated on, which is one: but on the part of the pullers there are many operations, because there are diverse impulses moving it."{1}

Moreover, all that under the opposite hypotheses is inexplicable, has, at least, a satisfactory explanation in the thesis that we are defending: and therefore for that reason alone, if there were no other, it ought to be preferred. In fact, if anyone asks why in chemical combination there is often a species of agitation or conflict or confusion between the combining substances, while everything goes peacefully, so to speak, in perfect crystallization, the reason is this: In chemical combination, the elements operate on each other with a force that ever changes their principle of activity. In crystallization the atoms or molecules have only to dispose themselves conformably with their angles and facets in a determinate, symmetrical order; to which accurate disposition of parts the impetus and violence often noticed in chemical combination would be hurtful. And if it be asked why a crystal may have its forms totally ruined by mechanical means, whilst a mixtum or compound never can be decomposed in that way, the answer is evident in the fact that in a crystal the atoms or molecules are suitably disposed, but not transformed. A merely mechanical cause, therefore, suffices to break them apart and spoil their symmetry; whereas in a mixtum or compound the elements are not only disposed in a certain manner, but also have their nature changed. To re-establish these in their former substantial being requires a cause contrary in effectiveness to that which transformed them. So can heat decompose a mixtum or compound, when it has force enough to take away in the principles of activity the change that happened at the moment of combination. So can another element do, with the concurrence of heat, and combine with an element that was with another or with others in the mixtum. In this way we can give a suitable reason for the facts: but to say that electricity, heat and other causes, which extrinsically concur in chemical combinations, can only shove atoms and make them group themselves by twos and threes, giving place to some and resisting others, is inexplicable and against experience.

{1} Contra Gent., ii. 57.

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