"For a large class of cases—though not for all—in which we employ the word 'meaning' it can be defined thus: the meaning of a word is its use in the language." (Part I, section 43)
Wittgenstein challenges the notion of fixity of meaning. He reacts strongly against the idea that all (or even most) words have a single fixed meaning that determines how they are used. According to Wittgenstein, use comes before meaning. In particular, he rebels against the idea that "meaning" is a mental state or process that accompanies the words we say. We do not need some inner criterion to fix the meanings of our words: so long as we all use words in the same way and can grasp how other people use words, then communication is unproblematic. Wittgenstein is hesitant to say that the meaning of a word is always its use in language because his attack on fixity of meaning carries with it the recognition that words can be put to a variety of different uses in different circumstances.