In naming objects, we are not establishing some organic relationship between the word and the object. It is only the use we make of the word in reference to the object that gives the word life. Similarly, giving a name to a particular feeling is worthwhile only if we can make use of that name. To identify a "particular expression" in a drawing or a "particular feeling" in a novel is not a matter of discovering something that we can then name. I do not discover a particular feeling by naming it, I produce a feeling that I would not experience if I had not named it. There is nothing more I can add to qualify what kind of particular feeling it is, any more than I can qualify what it is I see when I gesture at my general visual field and say, "I see this." In saying I have a particular feeling, I cannot say anything about the feeling because those words do nothing more than identify a feeling, just as an ostensive definition does not say anything about an object, but simply names it.
The distinction is between things that express something and things that express themselves. What the color pattern of a group of flowers says is different from what a person says. "The color pattern of the flowers says something" does not imply that I am thinking of what the flowers say. The color pattern says itself. There is nothing I want to add; I simply want to remark on the effect the colors have. If I say that the particular impression created by a picture is due to certain features in the picture, that does not mean I am any closer to naming the particular impression. I am saying that if these features were to change, the impression would change. Wittgenstein illustrates this idea with three faces drawn on page 180. He says that the impression created by a) is not changed in b), but is changed in c).
We are inclined to think that there is a particular feeling of familiarity, or a particular image that is a memory image. In fact, there is a wide family of feelings we refer to when we use the terms "familiarity and "memory image." We do not have feelings that are distinct from our expression of them that we must convey through the indirect medium of communication. There is no more direct expression of feeling to which we can aspire.
Wittgenstein draws an important distinction between things that express something else and things that express themselves. A paradigmatic example of something that expresses itself is a musical theme. We can use words to describe a musical theme, we can talk about the triumphant feeling it evokes, or the gentle calm it produces. Wittgenstein remarks, however, that we are repulsed by the suggestion that this is all that music does. Beethoven's Fifth Symphony does not exist in order to produce a triumphant feeling in us. If that were the case, we could take a drug that produces in us the same feeling as Beethoven's Fifth does, and that drug could then act as a substitute for the piece of music. This suggestion seems obscene because music is more than just the feeling it produces. Music expresses itself, not something else.
Similarly, if meaning what one says is simply a matter of a particular inner feeling at the time of speaking, we could imagine taking some sort of drug that might produce this inner feeling. This suggestion serves as a reductio ad absurdum. That is, Wittgenstein starts with a premise—that the "particular feeling" we might identify when we are sincere is the kind of feeling that we can describe, analyze, or name—and shows this premise to be false by deducing absurd consequences. If it were this kind of feeling, it is a physiological phenomenon, and thus something that could be studied by doctors or psychologists. If we could identify this physiological phenomenon as the result of certain kinds of neurons firing, we could plausibly concoct a drug that would induce this feeling.
The idea that a drug could induce the feeling of sincerity is absurd not because such a drug cannot be made, but because it is a grammatical impossibility. "Meaning" is not the kind of thing that we can talk about inducing. Wittgenstein suggests that the feeling of sincerity is simply an identifying marker that we can do no more than name. In this respect, it is like an ostensive definition. If I point to a chair and say, "this is a chair," there is no sense in asking, "what is this?" The word "this" does not tell us anything about the chair, it simply identifies that there is a chair. Similarly, identifying a "particular feeling" that accompanies meaning what one says does not tell us anything about the feeling, but simply identifies that there is a feeling. The reason we can say no more about the feeling is not because it is too vague for us to speak of. It is because we are not identifying anything definite in saying the feeling exists, just as we are not identifying anything definite when we say a face has an expression. The word "this," the expression on a face, and the feeling of sincerity all express themselves, they do not name something else.