Hume's argument, which suggests that we have reason to doubt the knowledge received from the senses, begins with an exploration of the continued existence of objects. He contends that since objects possess a continued existence, reality is not correctly perceived by the senses. As Hume says of the senses, "'tis evident these faculties are incapable of giving rise to the notion of the continu'd existence of their objects, after they no longer appear to the senses"(32). From this he concludes: "[t]hese faculties, therefore, if they have any influence in the present case, must produce the opinion of a distinct, not of a continu'd existence"(32). These contentions form the foundation of Hume's argument for doubting the knowledge received from the senses.
Hume describes how, since the world still exists when our senses are inoperable our senses cannot, and do not give us the whole truth about the world. He says, "I am naturally led to regard the world, as something real and durable, and as preserving its existence, even when it is no longer present to my perception"(35).
So, since "the mind looks farther than what immediately appears to it, its conclusions can never be put to the account of the senses"(32). This suggests that our mind sees a more accurate representation of the world than our senses, and that, as he says, our senses "must convey the impressions as those very existences, by a kind of fallacy and illusion"(32). Hume argues that the senses convey the information they receive of the external in such a way that would determine a distinct existence.
He continues by addressing the fundamental philosophical question of identity. He says that we are "so far from being able by our senses merely to determine this question, we must have recourse to the most profound metaphysics to...