V. DISCUSSIONS. ARISTOTLE ON THE LAW OF CONTRADICTION AND THE BASIS OF THE SYLLOGISM. ONE form of the Law of Contradiction is a thing cannot have opposite attributes at the same time. To understand the nature of this truth it is necessary to define what is meant by " opposite attributes". Examples are plentiful : white not-white; good not-good ; true not-true ; in general, A not-A. The second of each pair is not meant to include everything in the universe except the first of the pair ; for in that case the law of contradic- tion would not be true, since a thing can be at the same time white and not- white ; for example, it may be white and hard. The negative, therefore, not-A, must be restricted in its significa- tion to attributes within the region of A ; thus not- white is restricted to all colours, with the exception of white ; not-tri- angular to all figures except triangle. Within one region, there- fore, the individuals constituting it are incompatible. But what constitutes a region ? In the above examples, colour is one region, figure another ; and the region is denoted by a general term. But it can be easily seen that while what I have called region and what is known as class notion here go by the same name, colour or figure, they are not identical. The origin of the class notion is, so we are told, the similarity t of the individuals composing it ; but this similarity can be no explanation of their incompatibility which makes them members of the same region. Thus colours are incompatible a thing cannot be at the same time white and black ; but it is not in virtue of the similarity of white and black, which causes us to subsume them under the same general term colour, that they are incompatible. Moreover, not all class notions consist of incompatibles ; thus quality is a class notion, but not all qualities are incompatible. ^ This leads us to the question, Is it possible a priori to deternmie what attributes are incompatible ? Even if we could be justified in saying that all attributes of the same sense are incompatible, he truth of the statement could only be determined by experience. But it is evident that this is not true. Quality, intensity, and pitch all belong to the sense of hearing, and yet they are compat- ible ; colour and figure (plane) belong to the sense of sight, and et they are not incompatible. We are therefore justified in ying that experience alone can tell us what attributes are, and
