The Blue and Brown Books are transcripts of lecture notes Wittgenstein gave to his students in the early 1930s, shortly after returning to philosophy. They are so named because of the color of the paper they were originally bound in.
The Blue Book criticizes the idea that the meaning of a word resides in some sort of mental act or act of interpretation. Calling meaning a “mental” act is just a means of obscuring the matter. If the meaning of language is a matter of how we use words, we could just as easily say that meaning resides in the voice box as in the head. Rather than identify meaning with a mental act, Wittgenstein identifies meaning with use: the meaning of a word is determined by the way we use it and nothing more.
Wittgenstein attacks the philosophical “craving for generality” that leads philosophers to try to make the most general claims without properly considering particulars. This craving leads philosophers to make such general claims as the Heraclitean doctrine that “all is in flux.” Such claims amount to redefinitions: if all is in flux, for instance, the word stable ceases to have meaning. In their attempts to make grand metaphysical pronouncements, philosophers really just twist language out of shape.
Philosophers also often fail to distinguish between physical impossibility and grammatical impossibility, drawing on false analogies. If A has his mouth closed, it is physically impossible to know whether A has a gold tooth. Analogously, we might say that it is impossible to feel A’s toothache and conclude that the feeling of A’s toothache is a piece of knowledge to which we do not have access. In fact, feeling A’s toothache is a grammatical impossibility: the grammar of the word toothache is such that only the person who has the toothache can feel it. If we think that our knowledge is somehow incomplete because we are unable to feel the pains of others, we are simply showing that we have allowed ourselves to become confused about the grammar of certain words. Toothaches are things that people feel when they have them. Toothaches are not objects of knowledge that we can know or not know.
The Brown Book develops Wittgenstein’s concept of a “language game,” where he develops simpler forms of language to examine more closely the contrasts between different kinds of words. The upshot of these experiments is to show that most attempts to draw general theories of language are misguided and to draw our attention to the diversity of the uses and functions of words. Wittgenstein also examines the many different uses of such words as compare, recognize, and understand, showing that they have a variety of uses, all of which are related, but not in any definite way. He calls the relations between the various uses of a word family resemblances because, like the members of a family, the uses of a word share a certain resemblance but that resemblance is not based in any single feature.
The Brown Book contains a number of other significant ideas that are developed further in the Philosophical Investigations. Wittgenstein discusses rule following, arguing that there is no rock-bottom justification for the rules we follow and that we need not consciously follow or interpret a rule every time we obey a rule. He discusses the word can and the way that misunderstandings regarding this word give us mistaken notions about the past and future. He also discusses the distinction between seeing and seeing as, arguing that we can see a bunch of squiggles on a page as a face, but we cannot see a fork as a fork, since no alternative presents itself. In other words, when philosophers speak of seeing things “as themselves,” in the sense of seeing things in their essence, such statements have no meaning. For example, it would not make sense to speak of seeing someone “as a human being” or “as a person”—there’s no difference between that and how we normally see people.