The Confessions of Al Ghazzali by Mohammed Al-Ghazzali

I then examined what knowledge I possessed, and discovered that in none of it, with the exception of sense-perceptions and necessary principles, did I enjoy that degree of certitude which I have just described. I then sadly reflected as follows: “We cannot hope to find truth except in matters which carry their evidence in themselves—that is to say, in sense-perceptions and necessary principles; we must therefore establish these on a firm basis. Is my absolute confidence in sense-perceptions and on the infallibility of necessary principles analogous to the confidence which I formerly possessed in matters believed on the authority of others?