But, after all, who am I? What right have I to judge of these things? And what is it that determines my conclusions? If, subject to the impressions I receive, these are formed in direct consequence of those impressions, I trouble myself to no purpose in these investigations. It is necessary, therefore, to examine myself, to know what instruments are made use of in such researches, and how far I may confide in their use.
In the first place, I know that I exist, and have senses whereby I am affected. This is a truth so striking that I am compelled to acquiesce in it. But have I properly a distinct sense of my existence, or do I only know it from my various sensations? This is my first doubt; which, at present, it is impossible for me to resolve: for, being continually affected by sensations, either directly from the objects or from the memory, how can I tell whether my self-consciousness be, or be not, something foreign to those sensations, and independent of them.
My sensations are all internal, as they make me sensible of my own existence; but the cause of them is external and independent, as they affect me without my consent, and do not depend on my will for their production or annihilation. I conceive very clearly, therefore, that the sensation which is internal, and its cause or object which is external, are not one and the same thing.
Thus I know that I not only exist, but that other beings exist as well as myself; to wit, the objects of my sensations; and though these objects should be nothing but ideas, it is very certain that these ideas are no part of myself.
