Philosophical Investigations is divided into two parts, consisting of what Wittgenstein calls, in the preface, Bemerkungen, translated by G. E. M. Anscombe as "remarks".

[1] A survey among American university and college teachers ranked the Investigations as the most important book of 20th-century philosophy.

For Wittgenstein, his use of the term language-game "is meant to bring into prominence the fact that the speaking of language is part of an activity, or of a life-form.

[7] According to the use theory of meaning, the words are not defined by reference to the objects they designate or by the mental representations one might associate with them, but by how they are used.

[8] Wittgenstein's theory of meaning contrasts with Platonic realism[9] and with Gottlob Frege's notions of sense and reference.

This German sense of the word may help readers better understand Wittgenstein's context in his remarks regarding games.

Wittgenstein argues that definitions emerge from what he termed "forms of life", roughly the culture and society in which they are used.

[citation needed] It is this emphasis on becoming attentive to the social backdrop against which language is rendered intelligible that explains Wittgenstein's elliptical comment that "If a lion could talk, we could not understand him."

However, in proposing the thought experiment involving the fictional character Robinson Crusoe, a captain shipwrecked on a desolate island with no other inhabitant, Wittgenstein shows that language is not in all cases a social phenomenon (although it is in most cases); instead, the criterion for a language is grounded in a set of interrelated normative activities: teaching, explanations, techniques, and criteria of correctness.

We may see similar height, weight, eye color, hair, nose, mouth, patterns of speech, social or political views, mannerisms, body structure, last names, etc.

[18] It is perhaps important to note that this is not always a conscious process—generally we don't catalog various similarities until we reach a certain threshold, we just intuitively see the resemblances.

We've made a mistake in understanding the vague and intuitive rules that language uses and have thereby tied ourselves up in philosophical knots.

He suggests that an attempt to untangle these knots requires more than simple deductive arguments pointing out the problems with some particular position.

Instead, Wittgenstein's larger goal is to try to divert us from our philosophical problems long enough to become aware of our intuitive ability to see the family resemblances.

One general characteristic of games that Wittgenstein considers in detail is the way in which they consist in following rules.

[21] Rather, that one is following a rule or not is to be decided by looking to see if the actions conform to the expectations in the particular form of life in which one is involved.

[26] Wittgenstein also ponders the possibility of a language that talks about those things that are known only to the user, whose content is inherently private.

The usual example is that of a language in which one names one's sensations and other subjective experiences, such that the meaning of the term is decided by the individual alone.

For Wittgenstein, this is a grammatical point, part of the way in which the language-game involving the word "pain" is played.

[29] Although Wittgenstein certainly argues that the notion of private language is incoherent, because of the way in which the text is presented the exact nature of the argument is disputed.

That is, the only way to check to see if one has applied the symbol S correctly to a certain mental state is to introspect and determine whether the current sensation is identical to the sensation previously associated with S. And while identifying one's current mental state of remembering may be infallible, whether one remembered correctly is not infallible.

It is only in this way that it is interesting to talk about something like a "private language" — i.e., it is helpful to see how the "problem" results from a misunderstanding.

Another point that Wittgenstein makes against the possibility of a private language involves the beetle-in-a-box thought experiment.

Part of Wittgenstein's credo is captured in the following proclamation: "An 'inner process' stands in need of outward criteria.

According to Wittgenstein, those who insist that consciousness (or any other apparently subjective mental state) is conceptually unconnected to the external world are mistaken.

However, he is sure that it could not be the case that the external world stays the same while an "internal" cognitive change takes place.

[37] In his book Words and Things, Ernest Gellner was fiercely critical of the work of Ludwig Wittgenstein, J. L. Austin, Gilbert Ryle, Antony Flew, P. F. Strawson and many others.

Ryle refused to have the book reviewed in the philosophical journal Mind (which he edited), and Bertrand Russell (who had written an approving foreword) protested in a letter to The Times.

[40] Besides stressing the differences between the Investigations and the Tractatus, some critical approaches have claimed there to be more continuity and similarity between the two works than many suppose.

[41] In this work, Kripke uses Wittgenstein's text to develop a particular type of skepticism about rules that stresses the communal nature of language-use as grounding meaning.