According to Chao (1965):
Let us take an actual historical instance of a form being uttered, as when Mencius went to see King Huey of the state of Liang, who began with addressing him: “叟! Soou! ‘Sir!’” That was a token of the type 叟 soou, which occurred many times both before and after that particular instance. If we are interested in the particular occurrence as a historical event, with its linguistic as well as nonlinguistic circumstances, that constitutes a philological study. On the other hand, if we are interested in the soou as a type and the conditions under which it does or does not occur, especially in relation to contexts made up of other types, then it is a linguistic problem. Thus, philology is the study of tokens, and linguistics is the study of types.
Chao Y R. A grammar of spoken Chinese[M]. Univ of California Press, 1965.