Family resemblance

Family resemblance () is a philosophical idea made popular by Ludwig Wittgenstein, with the best known exposition given in his posthumously published book "Philosophical Investigations" (1953). It argues that things which could be thought to be connected by one essential common feature may in fact be connected by a series of overlapping similarities, where no one feature is common to all of the things. Games, which Wittgenstein used as an example to explain the notion, have become the paradigmatic example of a group that is related by family resemblances. It has been suggested that Wittgenstein picked up the idea and the term from Friedrich Nietzsche, who had been using it, as did many nineteenth century philologists, when discussing language families.
The first occurrence of the term "family resemblance" is found in Arthur Schopenhauer (1788–1860; "The World As Will and Representation §§17, 27, 28") who attributed the term to the school developed by Friedrich Wilhelm Joseph von Schelling (1775–1854). The next occurrence appeared in a note from 1930, commenting on Oswald Spengler's ideas. The notion itself features widely in Wittgenstein's later work, and in the "Investigations" it is introduced in response to questions about the general form of propositions and the essence of language – questions which were central to Wittgenstein throughout his philosophical career. This suggests that family resemblance was of prime importance for Wittgenstein's later philosophy; however, like many of his ideas, it is hard to find precise agreement within the secondary literature on either its place within Wittgenstein's later thought or on its wider philosophical significance.
Since the publication of the "Investigations", the notion of family resemblance has been discussed extensively not only in the philosophical literature, but also, for example, in works dealing with classification where the approach is described as "polythetic", distinguishing it from the traditional approach known now as "monothetic". Prototype theory is a recent development in cognitive science where this idea has also been explored. As the idea gained popularity, earlier instances of its occurrence were rediscovered e.g. in 18th-century taxonomy, in the writings of Lev Vygotsky or Władysław Tatarkiewicz.
Philosophical context.
The local context where the topic of family resemblances appears is Wittgenstein's critique of language. In "Philosophical Investigations" §65-71 the plurality of language uses is compared to the plurality of games. Next it is asserted that games have common features but no one feature is found in all of them. The whole argument has become famous under the heading 'language games'.
The larger context in which Wittgenstein's philosophy is seen to develop considers his uncompromising opposition to essences, mental entities and other forms of idealism which were accepted as a matter of fact in continental philosophy at the turn of the preceding century. In his view, the main cause for such errors is language and its uncritical use. In the received view, concepts, categories or classes are taken to rely on necessary features common to all items covered by them. Abstraction is the procedure which acknowledges this necessity and derives essences, but in the absence of a single common feature, it is bound to fail.
Terminology.
The term "Family resemblance" as feature of Wittgenstein's philosophy owes much to its translation in English. Wittgenstein, who wrote mostly in German, used the compound word 'Familienähnlichkeit', but as he lectured and conversed in English he used 'family likeness' (e.g. "The Blue Book", p. 17,33; "The Brown Book",§66). However, in the "Philosophical Investigations" the separate word 'Ähnlichkeit' has been translated as 'similarity' (§§11,130,185,444) and on two occasions (§§9,90) it is given as 'like'. The German family-word is common and it is found in Grimm's dictionary; a rare occurrence of 'family likeness' has been noted in a lecture by J. F. Moulton in 1877.
Examples and quotes.
Games are the main example considered by Wittgenstein in his text where he also mentions numbers and makes an analogy with a thread. He develops his argument further by insisting that in such cases there is not a clear cut boundary but there arises some ambiguity if this indefiniteness can be separated from the main point.
In §66 Wittgenstein invites us to 
The section mentions card games, board games, ball games, games like ring-a-ring-a-roses and concludes:
The following §67 begins by stating:
and extends the illustration
The problem of boundaries begins in §68
Formal models.
There are some simple models
which can be derived from the text of §66-9. The most simple one, which fits Wittgenstein's exposition, seems to be the sorites type. It consists in a collection of items "Item_1", "Item_2", "Item_3"... described by features A, B, C, D, ...:
"Item_1": A B C D 
"Item_2": B C D E 
"Item_3": C D E F 
"Item_4": D E F G 
"Item_5": E F G H 
In this example, which presents an indefinitely extended ordered family, resemblance is seen in shared features: each item shares three features with his neighbors e.g. "Item_2" is like "Item_1" in respects B, C, D, and like "Item_3" in respects C, D, E. Obviously what we call 'resemblance' involves different aspects in each particular case. It is also seen to be of a different 'degree' and here it fades with 'distance': "Item_1" and "Item_5" have nothing in common.
Another simple model is described as:
"Item_1": A B C 
"Item_2": B C D 
"Item_3": A C D 
"Item_4": A B D 
It exhibits the presence of a constant degree of resemblance and the
absence of a common feature without extending to infinity.
Wittgenstein rejects the disjunction of features or 'properties', i.e. the set {A,B,C,D..}, as something shared by all items. He admits that a 'sharing' is common to all but deems that it is only verbal:
Game studies.
Wittgenstein's suggestion (PI, §66) about the impossibility of formulating a definition of games portrays a predicament for disciplines, which entail games as their subject matter, because it denies the possibility to know what games are. One possible solution is to point out that Wittgenstein merely acts out his failing attempt to define the concept of game, because he wanted to demonstrate a mechanism of language. He wasn't particularly concerned about games, nor about the concept of 'game', but he was interested in the consequence of a definitory failure. The demonstration aims to show, that there is no reason to search for real definitions, which describe essential attributes of things, but rather nominal definitions, which describe the use of the term in a community. He connected this idea to language games – lingual expressions combined with action – as a more adequate alternative to explain the function of language. Confusing this is his choice to denominate the approach (PI, §7) as 'language games', further fueling the impression that he provides insights about the concept of game. Wittgenstein wasn't interested in games but in language, therefore his theories and examples are only superficially related to academic disciplines with games as subject matter.
Criticism and comments.
"Philosophical Investigations" is the primary text used in discussing family resemblances, even though the topic appears also in other works by Wittgenstein, notably "The Brown Book". Many contributions to the discussion are by people involved in philosophical research but concerned with more pragmatic questions such as taxonomy or information processing. Hans Sluga has observed that "the notion of family resemblance... draws on two quite different sets of ideas, two different vocabularies, but treats them as if they were one and the same. The first is the vocabulary of kinship, of descent, of some sort of real and causal connection.. the second is that of similarity, resemblance, affinity and correspondence."
Wittgenstein's insistence that boundaries do not really exist but can
be traced arbitrarily has been described as conventionalism and more generally the acceptance of his conception has been seen to present a refined nominalism.