There is a wonderful capacity that comes along with the ability to express ideas. Whatever we may want to say, we probably won't say exactly that. But in exchange, there is a chance of saying something else that is both good and new! After all, the thing we want to say — the structure p we're trying to describe — is not always a definite, fixed structure that our language-agents can easily read and copy. If p exists at all, it's likely to be a rapidly changing network involving several agencies. If so, then the language-agency may only be able to make guesses and hypotheses about p and try to confirm or refute them by performing experiments. Even if p were well defined in the first place, this very process is liable to change it, so that the final version q won't be the same as the original structure p. Sometimes we call this process thinking in words.
In other words, whether or not what you meant to say actually existed before you spoke, your language-agencies are likely either to reformulate what did exist or create something new and different from anything you had before. Whenever you try to express with words any complicated mental state, you're forced to oversimplify — and that can cause both loss and gain. On the losing side, no word description of a mental state can ever be complete; some nuances are always lost. But in exchange, when you're forced to separate the essences from accidents, you gain the opportunity to make reformulations. For example, when stuck on a problem, you may say to yourself things like Now, let's see — just what was I really trying to accomplish? Then, since your language-agency knows so little about the actual state of those other agencies it must answer such questions by making theories about them, and these may well leave you in a state that is simpler, clearer, and better suited to solving your problem.
When we try to explain what we think we know, we're likely to end up with something new. All teachers know how often we understand something for the first time only after trying to explain it to someone else. Our abilities to make language descriptions can engage all our other abilities to think and to solve problems. If speaking involves thinking, then one must ask, How much of ordinary thought involves the use of words? Surely many of our most effective thinking methods scarcely engage our language-agencies at all. Perhaps we turn to words only when other methods fail. But then the use of language can open entirely new worlds of thought. This is because once we can represent things in terms of strings of words, it becomes possible to use them in a boundless variety of ways to change and rearrange what happens in our other agencies. Of course, we never realize we're doing this; instead we refer to such activities by names like paraphrase or change of emphasis, as though we weren't changing what we're trying to describe. The crucial thing is that during the moments in which those word-strings are detached from their meanings, they are no longer subject to the constraints and limitations of other agencies, and the language-systems can do what they want with them. Then we can transmit, from one person's brain to another, the strings of words our grammar-tactics produce, and every individual can gain access to the most successful formulations that others can articulate. This is what we call culture — the conceptual treasures our communities accumulate through history.