 Instead of running through all of his opinions individually, he decides to place them in definite classes and examine one or two members of each particular class, in order to see whether he has any reason to doubt them. He defines the class of his opinions as those “I have acquired either from the senses or through the senses” (AT 7: 18, CSM 1: 12) and proceeds to further divide the class into (a) opinions about things “which are very small or in the distance”, about which he frequently errs; (b) opinions about his body and things that are in his immediate environment, which may be little more than a dream; (c) opinions about things, which even if they are imaginary, are at least fashioned out of things that are real, a 