We often take philosophy to be a matter of digging out what is hidden from view. When we think about it theoretically, language seems mysterious. It allows us to express thoughts and talk about the world, as if there were some direct correlation between the sentences we utter, the thoughts we have, and facts about the world. In logic, we find a world of pure, rigid relationships that we can apply to language, thought, and the world. Logic seems to contain the a priori order of things: it expresses all possibilities in the clearest manner, not clouded by any vagueness.
If language can be analyzed into perfect logical relationships, the sense of every sentence must be totally clear. Even sentences that may sound vague in ordinary speech must have a definite sense. This ideal of a logically perfect language eliminates all vagueness and uncertainty, but it also loses its connection to the vagueness and uncertainty we employ in everyday speech. Wittgenstein likens a world of ideal, logical forms to a smooth, frictionless surface as contrasted to the "rough ground" of ordinary language: "We have got on to slippery ice where there is no friction and so in a certain sense the conditions are ideal, but also, just because of that, we are unable to walk. We want to walk: so we need friction. Back to the rough ground!" (section 107). In order to make sense of how we actually use words, we must abandon this notion of ideal logical relationships and recognize there is no essence to language. "Language" is a series of more or less related family resemblances.
When we remove words like "knowledge," "proposition," and "being," from their ordinary use and then puzzle over what sorts of things they are independent of the contexts we find them in, we are bewitched by "pictures" that our language presses upon us. Wittgenstein's method is to describe how these words are used in their everyday contexts, and so show that the metaphysical questions we ask about them are not appropriate to the words as they are actually used. This method does not provide any great enlightenment, but only a sober sense of how little is achieved in metaphysical investigations. Philosophy does not tell us things we did not know; it reminds us of what we have always known by putting it clearly before our eyes. Philosophy should remind us of the ordinary use of the words that we puzzle about only when we extract them from their ordinary contexts. The methods he employs are thus like "therapies" that lead us out of metaphysical puzzlement.
We might think we have found a general definition of a proposition in saying that a proposition is the thing about which we can say it is true or false. But this simply describes how we talk about propositions: it does not explain anything about their deeper nature.
In criticizing the search for a logically ideal world of essences and rigid forms, Wittgenstein criticizes the position he himself espouses in the Tractatus. That text, which builds upon the earlier work of Frege and Russell, seeks to explain what language, thought, and the world must be like so that one can reflect the others. He develops what has been called the "picture theory of propositions," according to which propositions can depict the world by virtue of sharing a logical form with the facts they depict.
The remarks of sections 65–91 lead naturally into this criticism of his earlier view, as those sections attack the notion of essences and fixity of meaning. If words and sentences do not have to have a fixed sense, then how can we take them even to approximate rigid logical forms? The key to understanding language is not to identify the hidden structure of propositions but to appreciate how we actually use language to say what we need to say.