Kinds of Knowledge

43. A person who has a true idea simultaneously knows that he has a true idea, and cannot doubt of the truth of the thing perceived.

Proof: A true idea in us is an idea which is adequate in God, in so far as he is displayed through the nature of the human mind (2.11. Coroll.).

Let us suppose that there is in God, as he is displayed through the human mind, an adequate idea A.

The idea of this idea must also necessarily be in God.

It must be referred to him in the same way as the idea A (by 2.20, whereof the proof is of universal application).

But the idea A is supposed to be referred to God, as he is displayed through the human mind.

Therefore, the idea of the idea A must be referred to God in the same way.

That is (by 2.11 Coroll.), the adequate idea of the idea A will be in the mind, which has the adequate idea A.

Therefore he, who has an adequate idea or knows a thing truly (2.34), must at the same time have an adequate idea or true knowledge of his knowledge. Q.E.D.

Note: I explained in the note to 2.21. what is meant by the idea of an idea.

A person who has a true idea knows that a true idea involves the highest certainty.

For to have a true idea is only another expression for knowing a thing perfectly, or as well as possible.

No one can doubt of this, unless he thinks that an idea is something lifeless, like a picture on a panel, and not a mode of thinking or the very act of understanding.

Who can know that he understands anything, unless he do first understand it?

In other words, who can know that he is sure of a thing, unless he be first sure of that thing?

Further, what can there be more clear, and more certain, than a true idea as a standard of truth?

As light displays both itself and darkness, so truth is a standard both of itself and of falsity.

If a true idea is distinguished from a false idea as it is said to agree with its object, a true idea has no more reality or perfection than a false idea (since the two are only distinguished by an extrinsic mark);

Consequently, neither will a man who has a true idea have any advantage over him who has only false ideas.

Further, how can men have false ideas?

Lastly, how can anyone be sure, that he has ideas which agree with their objects?

The difference between a true idea and a false idea is plain.

A true idea is related to the false idea, as being is to not—being (2.35).

I have explained very clearly the causes of falsehood in 2.19. and 2.35 with the note.

It reveals the difference between a man who has true ideas, and a man who has only false ideas.

How can a man be sure that he has ideas that agree with their objects?

His knowledge arises from the simple fact, that he has an idea which corresponds with its object.

In other words, that truth is its own standard.

We may add that our mind, as it perceives things truly, is part of the infinite intellect of God (2.11. Coroll.).

Therefore, the mind’s clear and distinct ideas are as necessarily true as God’s ideas. –>

44. It is not in the nature of reason to regard things as contingent, but as necessary.

Proof: It is in the nature of reason to perceive things truly (2.41), namely (1. Ax. 6.), as they are in themselves—that is (1.29.), not as contingent, but as necessary. Q.E.D. –>

Corollary 1: It follows that it is only through our imagination that we consider things, whether in respect to the future or the past, as contingent.

The mind (2.17 and Coroll.) always regards things as present to itself, even though they do not exist, until some causes arise which exclude their existence and presence.

If the human body (2.18) has been affected by two external bodies simultaneously, the mind, when it afterwards imagines one of the said external bodies, will straightway remember the other.

That is, it will regard both as present to itself, unless there arise causes which exclude their existence and presence.

We imagine time, from the fact that we imagine bodies to be moved some more slowly than others, some more quickly, some at equal speed.

Thus, let us suppose that a child yesterday saw Peter for the first time in the morning, Paul at noon, and Simon in the evening; then, that today he again sees Peter in the morning.

As soon as he sees the morning light (2. Prop. 18), he will imagine that the sun will traverse the same parts of the sky, as it did when he saw it on the preceding day.

In other words, he will imagine a complete day.

Together with his imagination of the morning, he will imagine Peter; with noon, he will imagine Paul; and with evening, he will imagine Simon.

That is, he will imagine the existence of Paul and Simon in relation to a future time.

On the other hand, if he sees Simon in the evening, he will refer Peter and Paul to a past time, by imagining them simultaneously with the imagination of a past time.

If on some other evening, the child should see James instead of Simon, he will, on the following morning, associate with his imagination of evening sometimes Simon, sometimes James, not both together.

For the child is supposed to have seen, at evening, one or other of them, not both together.

His imagination will therefore waver.

With the imagination of future evenings, he will associate first one, then the other.

That is, he will imagine them in the future, neither of them as certain, but both as contingent.

This wavering of the imagination will be the same, if the imagination is concerned with things which we thus contemplate, standing in relation to time past or time present.

Consequently, we may imagine things as contingent, whether they be referred to time present, past, or future.

Corollary 2: It is in the nature of reason to perceive things under a certain form of eternity (sub quâdam æternitatis specie).

Proof: It is in the nature of reason to regard things, not as contingent, but as necessary (2.44).

Reason perceives this necessity of things (2.41) truly—that is (1. Ax. 6), as it is in itself.

But (1.16) this necessity of things is the very necessity of the eternal nature of God.

Therefore, it is in the nature of reason to regard things under this form of eternity.

We may add that the bases of reason are the notions (2.38), which answer to things common to all, and which (2.37) do not answer to the essence of any particular thing: which must therefore be conceived without any relation to time, under a certain form of eternity.