Remark
4
[23K]For the proposition to make sense, we will have to narrow down the scope of the variable to an appropriate set; in the first case, the set of human beings; in the second case, a numerical set (e.g. integers).
At this level of discussion, the concept of ”set” is intuitive; we will see later that there is an axiomatic theory of sets, almost universally used in Mathematics; however, even the intuitive concept of set is widely used (See remark [01J]).