That whenever the existence of a belief depends to some extent on us, then also the truth of that belief depends to some extent on us; in the sense in which this implies, that, when the existence of my belief that a shower will fall depends upon me, then, if this belief is true, I must have had a hand in making the shower fall: that, therefore, men must have had a hand in making to exist almost every fact which they ever believe to exist.
[1] Pragmatism: A New Name for some Old Ways of Thinking: Popular Lectures on Philosophy. By William James. Longmans, Green, and Co., 1907
[HUME'S PHILOSOPHY]
In both of his two books on the Human Understanding, Hume had, I think, one main general object. He tells us that it was his object to discover "the extent and force of human understanding," to give us "an exact analysis of its powers and capacity." And we may, I think, express what he meant by this in the following way. He plainly held (as we all do) that some men sometimes entertain opinions which they cannot know to be true. And he wished to point out what characteristics are possessed by those of our opinions which we can know to be true, with a view of persuading us that any opinion which does not possess any of these characteristics is of a kind which we cannot know to be so. He thus tries to lay down certain rules to the effect that the only propositions which we can, any of us, know to be true are of certain definite kinds. It is in this sense, I think, that he tries to define the limits of human understanding.
With this object he, first of all, divides all the propositions, which we can even so much as conceive, into two classes. They are all, he says, either propositions about "relations of ideas" or else about "matters of fact." By propositions about "relations of ideas" he means such propositions as that twice two are four, or that black differs from white; and it is, I think, easy enough to see, though by no means easy to define, what kind of propositions it is that he means to include in this division. They are, he says, the only kind of propositions with regard to which we can have "intuitive" or "demonstrative" certainty. But the vast majority of the propositions in which we believe and which interest us most, belong to the other division: they are propositions about "matters of fact." And these again he divides into two classes. So far as his words go, this latter division is between "matters of fact, beyond the present testimony of our senses, or the records of our memory," on the one hand, and matters of fact for which we have the evidence of our memory or senses, on the other. But it is, I think, quite plain that these words do not represent quite accurately the division which he really means to make. He plainly intends to reckon along with facts for which we have the evidence of our senses all facts for which we have the evidence of direct observation—such facts, for instance, as those which I observe when I observe that I am angry or afraid, and which cannot be strictly said to be apprehended by my senses. The division, then, which he really intends to make is (to put it quite strictly) into the two classes—(1) propositions which assert some matter of fact which I am (in the strictest sense) observing at the moment, or which I have so observed in the past and now remember; and (2) propositions which assert any matter of fact which I am not now observing and never have observed, or, if I have, have quite forgotten.
We have, then, the three classes—(1) propositions which assert "relations of ideas"; (2) propositions which assert "matters of fact" for which we have the evidence of direct observation or personal memory; (3) propositions which assert "matters of fact" for which we have not this evidence. And as regards propositions of the first two classes, Hume does not seem to doubt our capacity for knowledge. He does not doubt that we can know some (though, of course, not all) propositions about "relations of ideas" to be true; he never doubts, for instance, that we can know that twice two are four. And he generally assumes also that each of us can know the truth of all propositions which merely assert some matter of fact which we ourselves are, in the strictest sense, directly observing, or which we have so observed and now remember. He does, indeed, in one place, suggest a doubt whether our memory is ever to be implicitly trusted, but he generally assumes that it always can. It is with regard to propositions of the third class that he is chiefly anxious to determine which of them (if any) we can know to be true and which not. In what cases can any man know any matter of fact which he himself has not directly observed? It is Hume's views on this question which form, I think, the main interest of his philosophy.