Page:Mind (New Series) Volume 6.djvu/522

 506 HUGH MACCOLL: Diagrammatic Illustrations. The accompanying figures will help us to understand, and fix in our mind, the meanings of the symbols a : /3,, a + fi, aft, and others which we . " have been discussing in the preceding pages. He I Fie 4 FIG 2 Fie 3 ' AB Consider first Fig. 1. Let the collection of points in the circle E be our universe of discourse, all points not included in E being left out of account. Let a point P be taken at random in the collection E, and let the symbols e, a, /3, respectively assert that P will belong to the collection E, that it will belong to the collection A, that it will belong to the collection B. From the disposition of the circles in the case we are considering (Fig. 1), this random point P may or may not turn out to be in A, and it may or may not be in B, so that the statements a and /3 may be true or false ; and if the experiment be repeated often enough, each of the two statements will be sometimes true and sometimes