At the beginning of his recent book, The Mathematics of Collective Action, James Coleman distinguishes two "quite different streams of work in the study of social action" (Coleman, 1973, p. 1). Within the first stream man's behaviour is explained as response to his environment. Causal factors and processes are sought, in that the behaviour is seen as a response called forth by some more or less complicated stimulus. The second stream conceives of behaviour as pursuit of goals, as actions to be explained according to quite a different pattern. Coleman adds in a note that in addition to these two directions of work, which begin at the level of the individual, there are "those, like sociological functionalism and certain parts of ecology, that begin at the level of the collectivity" (Coleman, 1973, p. 1, n. 1).