Extension refers to all things with essential attributes reflected by food, that is, the scope of application of other concepts related to it.
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 "commodity" is "labor products produced for exchange"; The extension of a term is the kind of thing that a term refers to. For example, the extension of "person" is the kind that everyone has been making 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 words "S" and "P" that can be used as the subject and predicate of an outspoken proposition.