 In other words, when viewed as being mental, a thought or idea may have associated with it other thoughts or ideas that seem related even though, when viewed as being physical, they have very little in common. As Russell explains, “In my mind, Caesar may call up Charlemagne, whereas in the physical world the two were widely sundered” (CP, Vol. 7, 15). Even so, it is a mistake, on this view, to postulate two distinct types of thing (the idea of Caesar and the man Caesar) that are composed of two distinct substances (the mental and the physical). Instead, “The whole duality of mind and matter, according to this theory, is a mistake; there is only one kind of stuff out of which the world is made, and this stuff is called mental in one arrangement, physical in the other” (CP, Vol. 7, 15).