This sceptical doubt, both with respect to reason and the senses, is a malady which can never be radically cured, but must return upon us every moment, however we may chase it away, and sometimes may seem entirely free from it. 'Tis impossible, upon any system, to defend either our understanding or senses; and we but expose them farther when we endeavour to justify them in that manner. As the sceptical doubt arises naturally from a profound and intense reflection on those subjects, it always increases the farther we carry our reflections, whether in opposition or conformity to it. Carelessness and inattention alone can afford us any remedy. For this reason I rely entirely upon them; and take it for granted, whatever may be the reader's opinion at this present moment, that an hour hence he will be persuaded there is both an external and internal world; and, going upon that supposition, I intend to examine some general systems, both ancient and modern, which have been proposed of both, before I proceed to a more particular inquiry concerning our impressions. This will not, perhaps, in the end, be found foreign to our present purpose. [1] Part II. Sect. 6. [2] Sect. 5. [3] Part II. Sect. 4. [4] Part II. Sect. 5. [5] Part. II. Sect. 5. [6] This reasoning, it must be confessed, is somewhat abstruse, and difficult to be comprehended; but it is remarkable, that this very difficulty may be converted into a proof of the reasoning. We may observe, that there are two relations, and both of them resemblances, which contribute to our mistaking the succession of our interrupted perceptions for an identical object. The first is, the resemblance of the perceptions: the second is, the resemblance which the act of the mind in surveying a succession of resembling objects, bears to that in surveying an identical object. Now these resemblances we are apt to confound with each other; and 'tis natural we should, according to this very reasoning. But let us keep them distinct, and we shall find no difficulty in conceiving the precedent argument. [7] Sect. 6. [8] Sect. 5. SECTION III. OF THE ANCIENT PHILOSOPHY.