Proceeding further, we must set forth a major theorem of
functional analysis; just as the same item may have multiple functions,
so may the same function be diversely fulfilled by alternative items.
Functional needs are here taken to be permissive, rather than determinant,
of specific social structures. Or, in other words, there is a range
of variation in the structures which fulfill the function in question.
(The limits upon this range of variation involve the concept of structural
constraint, of which more presently) (1968, pp. 87-88).