In the previous discussion no attempt was made to define “about” the expression “is about” was merely a synonym for “cover”. That is, “what a document is about” was used to mean the same as “what a document covers”. These expressions may not be very precise and the terms “about” and “cover” are not easily defined. Nevertheless, they are expressions that seem acceptable to most people and to be understood by them. It is not my intention to enter into a philosophical discussion on the meaning of “about” or “aboutness”. A number of authers have already done so. In so doing, they have failed to clarify the situation, at least as far as the task of subject indexing is concerned. Beghtol (1986) and Hutchins (1978) both draw upon text linguistics in discussing the subject, Maron (1977) adopts a probabilistic approach, and Swift et al. (1978) are careful to point out that aboutness in indexing may not coincide with the aboutness that searchers for information are concerned with. Wilson (1968) goes so far as to imply that subject indexing faces “intractable” problems because it is so difficult to decide what a document is about.