Plato 3

Where does certain knowledge come from ?

Some things seem capable of proof.

Proof that the two marked angles are the same.

Is this an example of a priori knowledge? Are there others?

A priori knowledge is knowledge you have independently of any experience.

It is contestable whether there can be such. There is the view: everything you know has to come from what you are told, or what you find out by looking - by observing, by experimenting.

Those who believe there is such a thing have in mind a variety of examples.

Theories about the possibility of a priori knowledge.

1. Plato

Plato's theory is that we do have a priori knowledge and that we bring it with us from an earlier existence...

SOCRATES: Then he who does not know [the slave boy before Socrates has brought his 'knowledge' to the surface] may still have true notions of that which he does not know?

MENO: He has.

SOCRATES: And at present these notions have just been stirred up in him, as in a dream; but if he were frequently asked the same questions, in different forms, he would know as well as any one at last?

MENO: I dare say.

SOCRATES: Without any one teaching him he will recover his knowledge for himself, if he is only asked questions?

MENO: Yes.

SOCRATES: And this spontaneous recovery of knowledge in him is recollection?

MENO: True.

SOCRATES: And this knowledge which he now has must he not either have acquired or always possessed?

MENO: Yes.

...

And I am certain that no one ever did teach him.

SOCRATES: And yet he has the knowledge?

MENO: The fact, Socrates, is undeniable.

SOCRATES: But if he did not acquire the knowledge in this life, then he must have had and learned it at some other time?

MENO: Clearly he must.

Plato, Meno, 85c

What other theories are there?

2. A priori knowledge consists of analytic truths

Eg Brothers are male

[Male + sibling] includes [male]

Male = male

3. We can work out that experience is possible only if we possesses certain concepts, and we can work out what these these concepts must be.

For example, could we have any experience if we didn't have the concept of time?

Or could we imagine what such experience would be like?

Could we have experience at all if we didn't have the concept of space?

Is it possible to imagine what experience would be like if we didn't have the concept of space?

These are the type of questions pursued by Kant.

There is a priori knowledge. It takes the form of truths about what concepts are presupposed by our having experience.

4. There are some truths (eg mathematical truths, logical truths) to which our reason gives us partial access.

5. Mathematical and logical truths are empirical generalisations - there is no a priori knowledge.