To begin with, Descartes notes that many of his beliefs are derived from his senses, or from perception. He notes that the senses, however, can often mislead. A stick may look bent when viewed half submerged in water, the true size of the sun and the moon is many times greater than would appear from sight, and so on. One can even suffer hallucinations such that what one thinks to be there does not exist at all. Descartes resolves not to trust completely that which has deceived him once, and therefore rejects any information from the senses as being uncertain and fallible.
