Hume, 1711, was a classic empiricist. In this essay I will explain and illustrate Hume’s fork. But to begin with, I shall define empiricism. It is the belief that all ideas come from experience. Hume goes further and says that empiricism is indeed experience and they all come from what he calls ‘impressions’. Hume’s such ‘impressions’ are experiences, granted; but some of these impressions come from within ourselves as opposed to the five exterior senses. Second, he thinks that all justified beliefs are justified through experience, except for what he called ‘relations of ideas’. What relations of ideas are, are simply how our ideas are related to one another. So, for example, you could know that all bachelors are unmarried without interviewing any bachelors to find out their marital status, because that is a matter of how we define the word "bachelor." He also asserts that all mathematical knowledge is just the knowledge of definitions. But we can't know anything about, say, whether something exists or not based on how we define the word. And so Hume attempts like the ontological argument does, to show that God must exist because of the way we define "God," are bound to fall flat. On the other hand, any knowledge that might lead us to conclude anything about what is real outside of our own minds, according to Hume, has got to come from experience. But in order to understand Hume’s fork, there are two types of propositions that are both very different, we must distinguish between them.
There are synthetic propositions that are true by observation or by verification. So using as an example - the cat is on the mat. We can see, with our eyes, that the cat is on the mat. One can identify the validity of this statement by observing it. A proposition is said to have ‘truth functionality’ but we can say this s true as we can see it. Thus the truth comes from observation; we can SEE that cat, we can verify the claim that the cat is on