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


THAT in mixed or composite bodies the transformation produces another nature totally different from the nature of its components, is so evident to the senses that it has no need of further proof. Hence it is a universal and rooted belief. A man of plain common sense would laugh if you said to him, "You must know that which you suppose to be water is nothing of the sort, but only what two other substances, quite different, seem to be, just as a circular piece of wood with seven colours painted on it seems white, if you turn it round very fast." Nature tells us the contrary, and language, that faithfully interprets the common sentiments of mankind, confirms the same truth. It has always been said, and is said by learned and ignorant, that the chemical compound has a new nature, a nature different from that of its elements. The chemists also say the same, even those who deny it theoretically and think that in the mixtum or compound the elements remain just as they were before the combination. Moreover, the words "unity of nature" mean unity of the active principle, not a co-operation of different operators for one and the same end.

To this common language St. Thomas appealed when showing, against Eutyches, that in Christ there cannot be one nature only, because the divine and the human nature are permanent in Him. A one results from many, he says, firstly in virtue of order only, as one city is composed of many houses, and one army out of many soldiers. Secondly, in virtue of order and composition; as one house is made of many parts by mutual contact and joining. But these ways, he says, "will not suffice to make one nature from many: and therefore those things whose form is only order and composition are not natural in such a way that their unity may be called unity of nature." He goes on to say "Never is it found that one nature comes to be, out of two natures remaining such, because each nature is a whole, and those things out of which anything is constituted have the relation of parts. Wherefore, since the result of the soul's union with the body is one individual, neither the body nor the soul can be said to be a nature in the sense in which we are now using the word, because neither the one nor the other has a complete species, but each is a part of one nature. Therefore, since human nature and the Divine Nature are each a complete nature, it is impossible for them to concur in making one nature, without one or both ceasing to be which is not possible, because it is evident from what has been said that one Christ is true God and true man. It is therefore impossible that in Christ there can be one nature only."{1}

Here we can see incidentally what mischief may be done by an easy twisting of words from the sense in which they are commonly understood, for the purpose of furthering particular opinions. Those therefore who will not allow that the nature of the elements is changed in the mixtum or compound, should call the compound an aggregate or a mingling together or anything they please, but not a new nature; or they will not only come into collision with words that are used and must be used in Theology, but also be at variance with the common language of mankind.

{1} Contra Gent., iv. 3.5.

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