Sources of information include: logic and reason teachings of authoritative, trustworthy people the senses articles of faith: mystical experiences, mystical experiences give knowledge but can"t be explained in words/languages. Knowledge is not transferring but seeing things already inside you. Al-ghazali calls beliefs into doubts with the words accidental beliefs imposed on him . If your beliefs are shaky, find beliefs both secure and reliable. How do you go about testing beliefs: test 1: take the belief and ask, is it unshakeable by miracle workers? . The moral is that things learned by authority fail this test. Al-ghazali thinks that the two things that pass this test are: sense perceptions, necessary principles (basic rules of logic, processing things) However, even with sense perceptions, we can"t trust all that we see: example. Stars in the night sky might seem the size of small coins to our eyes, but in actuality, they have a possibility of being larger than our planet.