One of the most fundamental of philosophical errors is to suppose that since things are known by us in a certain way, they must exist in themselves in that very same way. St. Thomas raises an objection concerning the human mode of knowing:
It would seem that our intellect does not understand corporeal and material things by abstraction from the phantasms. For the intellect is false if it understands an object otherwise than as it really is. Now the forms of material things do not exist as abstracted from the particular things represented by the phantasms. Therefore, if we understand material things by abstraction of the species from the phantasm, there will be error in the intellect.
He responds to the objection:
Abstraction may occur in two ways:
First, by way of composition and division; thus we may understand that one thing does not exist in some other, or that it is separate therefrom.
Secondly, by way of simple and absolute consideration; thus we understand one thing without considering the other. Thus for the intellect to abstract one from another things which are not really abstract from one another, does, in the first mode of abstraction, imply falsehood. But, in the second mode of abstraction, for the intellect to abstract things which are not really abstract from one another, does not involve falsehood, as clearly appears in the case of the senses. For if we understood or said that color is not in a colored body, or that it is separate from it, there would be error in this opinion or assertion. But if we consider color and its properties, without reference to the apple which is colored; or if we express in word what we thus understand, there is no error in such an opinion or assertion, because an apple is not essential to color, and therefore color can be understood independently of the apple. Likewise, the things which belong to the species of a material thing, such as a stone, or a man, or a horse, can be thought of apart from the individualizing principles which do not belong to the notion of the species. This is what we mean by abstracting the universal from the particular, or the intelligible species from the phantasm; that is, by considering the nature of the species apart from its individual qualities represented by the phantasms. If, therefore, the intellect is said to be false when it understands a thing otherwise than as it is, that is so, if the word “otherwise” refers to the thing understood; for the intellect is false when it understands a thing otherwise than as it is; and so the intellect would be false if it abstracted the species of a stone from its matter in such a way as to regard the species as not existing in matter, as Plato held. But it is not so, if the word “otherwise” be taken as referring to the one who understands. For it is quite true that the mode of understanding, in one who understands, is not the same as the mode of a thing in existing: since the thing understood is immaterially in the one who understands, according to the mode of the intellect, and not materially, according to the mode of a material thing.
The objection basically argues that it is impossible to know things in a general way, since things do not exist in reality in a general way, but in a particular way. So if they are understood generally, they are understood falsely.
St. Thomas’s response is that it would be false, if someone were to assert, “tables exist in reality in a general way,” but that it is not false to have a general understanding of tables without asserting that tables are general things.
While error can arise in many ways, this kind of confusion between how things are known and how they are is one of the most basic causes of human error, both in regard to speculative and to practical truth. I will look at some examples in a later post.