presents us, be ever received as true pictures of past perceptions. The memory, senses, and understanding are therefore all of them founded on the imagination, or the vivacity of our ideas. No wonder a principle so inconstant and fallacious should lead us into errors when implicitly followed (as it must be) in all its variations. 'Tis this principle which makes us reason from causes and effects; and 'tis the same principle which convinces us of the continued existence of external objects when absent from the senses. But though these two operations be equally natural and necessary in the human mind, yet in some circumstances they are directly contrary;[17] nor is it possible for us to reason justly and regularly from causes and effects, and at the same time believe the continued existence of matter. How then shall we adjust those principles together? Which of them shall we prefer? Or in case we prefer neither of them, but successively assent to both, as is usual among philosophers, with what confidence can we afterwards usurp that glorious title, when we thus knowingly embrace a manifest contradiction? This contradiction[18] would be more excusable were it compensated by any degree of solidity and satisfaction in the other parts of our reasoning. But the case is quite contrary. When we trace up the human understanding to its first principles, we find it to lead us into such sentiments as seem to turn into ridicule all our past pains and industry, and to discourage us from future inquiries. Nothing is more curiously inquired after by the mind of man than the causes of every phenomenon; nor are we content with knowing the immediate causes, but push on our inquiries till we arrive at the original and ultimate principle. We would not willingly stop before we are acquainted with that energy in the cause by which it operates on its effect; that tie, which connects them together; and that efficacious quality on which the tie depends. This is our aim in all our studies and reflections: and how must we be disappointed when we learn that this connexion, tie, or energy lies merely in ourselves, and is nothing but that determination of the mind which is acquired by custom, and causes us to make a transition from an object to its usual attendant, and from the impression of one to the lively idea of the other? Such a discovery not only cuts off all hope of ever attaining satisfaction, but even prevents our very wishes; since it appears, that when we say we desire to know the ultimate and operating principle as something which resides in the external object, we either contradict ourselves, or talk without a meaning.