Thinking, believing, and wishing are perfectly natural and unproblematic activities. The difficulty comes when we wonder retrospectively how they are possible. An order, a belief, etc., contain a picture of what it is they represent, but how do we apply these pictures to reality? I can order a person to raise his arm, do it myself as an example, and urge him on in all sorts of different ways, but none of these actions guarantee that he will understand. I cannot convey the picture itself, but only try to represent it by other means.
How do I know a wish is a wish, and that an expectation is an expectation? If these are unsettled feelings that are satisfied when the wish or expectation is met, I have no way of knowing what I wish or expect until the feeling is satisfied. And if it is a mental picture of the wish or expectation being fulfilled, there remains uncertainty as to what occurrence corresponds with the picture.
The meaning of a sentence cannot simply be a picture: we must also know how to apply that picture. The application connects the picture with the thing itself. But how does an order connect with its execution, if unfulfilled orders never have an execution?
We tend to say that we believe fire burns because of past experience. But this belief is not based on reasons, as is my belief that the stock market will plummet. It is more akin to my belief that past experience can inform me about future experience. I can give countless reasons for holding this belief, but none of them explain why I hold it. I do not assume these beliefs, either. Someone who claims not to believe such things is simply unintelligible. Certain claims stand beyond justification.
Language is not just a means of communication. Its sole purpose is not to create understanding in another person. Words are not a lifeless medium through which we transmit living, bodiless "meanings" from one person to another. The sense of a sentence relies as much on custom and context as it does on the specific meanings of different words. Understanding a sentence is much like understanding a musical theme. Though a theme can arouse certain thoughts or feelings, we cannot define that as its purpose: we understand the music (or in a sentence, the words), not its meaning.
Does "one" in "this rod is one yard long" have a different meaning from "one" in "here is one soldier"? This depends on the context of the question. The word has the same meaning if compared to a word like "saw," which has two meanings, but it has two different meanings if we emphasize that it is used first as a measure and second as a numeral. The word "not" presents similar ambiguities.