Introduction of connotation and extension

According to traditional logic, the connotation of a word is its meaning, that is, its concept, which reflects the unique attributes of things. For example, the connotation of a commodity is a labor product produced for exchange; The extension of a term is the kind of thing that a term refers to. For example, the extension of people is the kind that everyone has made up through the ages. As one of the textbooks of modern logic, Bohr-Royal Logic first put forward the difference between connotation and extension. Although later logicians have different views on the rationality of this distinction, the terms connotation and extension have been used to this day. The extension relation of traditional logic Because traditional logic does not consider empty classes, there are only five possible relations between the extension classes S and P of any two items S and P that can be used as the subject and predicate of an outspoken proposition. They can be represented by Euler diagram as follows: