Ambiguity

By instinct humans yearn for reassurance and certainties and dream of an orderly universe where the reasoning process corresponds to external reality. This attitude is reflected by the assumption, authoritatively legitimized by Aristotle (384–322 B.C.E.), that no responsible statement can exhibit internal contradictions. In his Categories, Aristotle states that the essential character of a substance seems to be its ability to host opposites. At any instant, however, one can assign either a quality or its opposite to a substance: According to Aristotle, "Nobody can be simultaneously sick and healthy. Similarly, nothing is at the same time white and black. No object exists simultaneously hosting opposites." No alternatives exist besides these two; any third possibility is excluded: tertium non datur.