Everything, it is said, must have a cause; for if anything wanted a cause, it would produce itself; that is, exist before it existed; which is impossible. But this reasoning is plainly inconclusive; because it supposes that in our denial of a cause we still grant what we expressly deny, viz. that there must be a cause; which therefore is taken to be the object itself; and that, no doubt, is an evident contradiction.
An object, that exists absolutely without any cause, certainly is not its own cause; and when you assert, that the one follows from the other, you suppose the very point in questions and take it for granted, that 'tis utterly impossible anything can ever begin to exist without a cause, but that, upon the exclusion of one productive principle, we must still have recourse to another.
Whatever is produced without any cause, is produced by nothing; or in other words, has nothing for its cause. But nothing can never be a cause, no more than it can be something, or equal to two right angles. By the same intuition, That we perceive nothing not to be equal to two right angles, or not to be something, we perceive, that it can never be a cause; and consequently must perceive, that every object has a real cause of its existence.
To give an instance of this, we may chose any point of history, and consider for what reason we either believe or reject it. Thus we believe that Caesar was killed in the senate-house on the ides of March; and that because this fact is established on the unanimous testimony of historians, who agree to assign this precise time and place to that event. Here are certain characters and letters present either to our memory or senses; which characters we likewise remember to have been used as the signs of certain ideas; and these ideas were either in the minds of such as were immediately present at that action, and received the ideas directly from its existence; or they were derived from the testimony of others, and that again from another testimony, by a visible gradation, 'till we arrive at those who were eyewitnesses and spectators of the event. It’s obvious all this chain of argument or connection of causes and effects, is at first founded on those characters or letters, which are seen or remembered, and that without the authority either of the memory or senses our whole reasoning would be chimerical and without foundation. Every link of the chain would in that case hang upon another; but there would not be anything fixed to one end of it, capable of sustaining the whole; and consequently there would be no belief nor evidence. And this actually is the case with all hypothetical arguments, or reasoning upon a supposition; there being in them, neither any present impression, nor belief of a real existence.
It is no just objection to the present doctrine, that we can reason upon our past conclusions or principles, without having recourse to those impressions, from which they first arose. For even supposing these impressions should be entirely effaced from the memory, the conviction they produced may still remain; and 'tis equally true, that all reasoning concerning causes and effects are originally derived from some impression; in the same manner, as the assurance of a demonstration proceeds always from a comparison of ideas, though' it may continue after the comparison is forgot.
(From A TREATISE OF HUMAN NATURE, BOOK I. of the Understanding, PART III. OF KNOWLEDGE AND PROBABILITY by David Hume)