Wittgenstein expounds his notion of a family resemblance in two important passages. The first is from
The Blue Book:
This craving for generality is the resultant of a number of tendencies connected with particular philosophical confusions. There is—
(a) The tendency to look for something common to entities which we commonly subsume under a general term. We are inclined to think that there must be something common to all games, say, and that this common property is the justification for applying the general term “game” to the various games; whereas the games form a
familythe members of which have family likenesses ….
(b) There is a tendency rooted in our usual forms of expression, to think that a man who has learnt to understand a general term, say, the term “leaf,” has thereby come to possess a kind of general picture of a leaf, as opposed to pictures of particular leaves …. This again is connected with the idea that the meaning of a word is an image, or a thing correlated with the word.