Part I, Chapter 2: Of Ideas in relation to their Objects
ALL that we conceive is represented to our mind, either as a thing, or as a manner of a thing, or as a thing modified.
I call a thing that which we conceive as subsisting by itself, and as the subject of all which we conceive of it. This is otherwise termed substance.
I call manner of a thing, or mode, or attribute, or quality, that which, being conceived in the thing, and as not able to subsist without it, determines it to be of a certain fashion, and to be so denominated.
I call a thing modified when I consider the substance as determined in a certain manner or mode.
This will be better comprehended by a few examples. When I consider a body, the idea which I have of it represents to me a thing, or a substance, because I consider it as a thing which subsists by itself, and which needs no other subject in order to exist. But when I consider that this body is round, the idea which I have of roundness re-rally exist; not that We cannot conceive the mode without giving a distinct and express attention to its subject, but what shows that the notion of relation to a substance is involved, at least confusedly, in that of mode, is, that we are not able to deny that relation of mode without destroying the idea which we had of it, whereas, when we conceive two things as two substances, we may deny the one of the other, without destroying the ideas which we had of each. For example, I am able clearly to conceive prudence without paying distinct attention to a man who may be prudent; but I cannot conceive prudence in denying the relation which it has to a man, or to some other intelligent nature which may have that virtue; and, on the contrary, when I have considered all that belongs to an extended substance, which is called body, as extension, figure, mobility, divisibility; and when, on the other hand, I consider all that belongs to the mind, and to substance which thinks, as thinking, doubting, remembering, willing, reasoning, I can deny of the substance extended all that I conceived of the substance which thinks, without ceasing, on that account, to conceive very distinctly the substance extended, and all the other attributes which are joined to it; and I can reciprocally deny of the substance which thinks, all that I have conceived of the substance extended, and, nevertheless, conceive very distinctly all which I had conceived of the substance which thinks. This proves, likewise, that thought is not a mode of substance extended, since extension, and all the properties which belong to it, may be denied of thought, while we are still able to conceive thought very clearly.
It may be remarked, on the subject of modes, that there are some which may be called internal, because they are conceived to be in the substance, as round, square; and others which may be called external, because they are taken from something which is not in the substance, as loved, seen, desired, which are names taken from the actions of another,—and this is what is called in the schools external denomination; and if these modes are taken from some manner in which we conceive things, they are called second intentions. Thus, being subject, being attribute, are second intentions, because they are modes under which we conceive things, which are obtained from the operation of the mind, which has connected together two ideas in affirming the one of the other. It may be remarked, further, that there are some modes which may be called substantial, because they represent to us true substances, applied to other substances as their modes and manners; clothed, armed, are modes of this sort. There are others which may be called simply, real; and these are the true modes, which are not substances, but manners of substance. There are, finally, some which may be called negative, because they represent to us substance, with a negation of some mode, real or substantial.
And if the objects represented by these ideas, whether substances or modes, be really such as they are represented to us, they are called true; and if they are not such, they are false, in the way which they may be, and these are what are called in the schools beings of reason (entia rationis), which consist commonly in the union which the mind makes of two ideas real in themselves, but which are not truly connected together so as to form a single idea; and as when we may form to ourselves a mountain of gold, it is a being of reason, because it is composed of two ideas—of a mountain, and of gold, which it represents as united, though they are not really so.