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however, are intelligible only so far as we make them actually so by abstracting them from material conditions, it is clear that those substances are more intelligible in themselves whose nature is immaterial. Therefore they are much more known to us than are material things.
Obj. 4: Further, the Commentator says (Metaph. ii) that "nature would be frustrated in its end" were we unable to understand abstract substances, "because it would have made what in itself is naturally intelligible not to be understood at all." But in nature nothing is idle or purposeless. Therefore immaterial substances can be understood by us.
Obj. 5: Further, as sense is to the sensible, so is intellect to the intelligible. But our sight can see all things corporeal, whether superior and incorruptible; or lower and corruptible. Therefore our intellect can understand all intelligible substances, even the superior and immaterial.
_On the contrary,_ It is written (Wis. 9:16): "The things that are in heaven, who shall search out?" But these substances are said to be in heaven, according to Matt. 18:10, "Their angels in heaven," etc. Therefore immaterial substances cannot be known by human investigation.
_I answer that,_ In the opinion of Plato, immaterial substances are not only understood by us, but are the objects we understand first of all. For Plato taught that immaterial subsisting forms, which he called "Ideas," are the proper objects of our intellect, and thus first and _per se_ understood by us; and, further, that material objects are known by the soul inasmuch as phantasy and sense are mixed up with the mind. Hence the purer the intellect is, so much the more clearly does it perceive the intelligible truth of immaterial things.
But in Aristotle's opinion, which experience corroborates, our intellect in its present state of life has a natural relationship to the natures of material things; and therefore it can only understand by turning to the