John Stuart Mill and Timothy Williamson both analogize the role of language in philophical inquiry to the role of telescopes in astronomical inquiry. I don’t know that I have anything particularly illuminating to say about this shared analogy, but I thought I would reproduce the relevant passages here.
First, here are the first two paragraphs from chapter one of Mill’s System of Logic (titled: “Of the Necessity of Commencing with an Analysis of Language”):
“It is so much the established practice of writers on logic to commence their treatises by a few general observations (in most cases, it is true, rather meagre) on Terms and their varieties, that it will, perhaps, scarcely be required from me in merely following the common usage, to be as particular in assigning my reasons, as it is usually expected those who deviate from it.
The practice, indeed, is recommended by considerations far too obvious to require a formal justification. Logic is a portion of the Art of Thinking: Language is evidently, and by the admission of all philosophers, one of the principal instruments or helps of thought; and any imperfection in the instrument, or in the mode of employing it, is confessedly liable, still more than in almost any other art, to confuse and impede the process, and destroy all ground of confidence in the result. For a mind not previously versed in the meaning and right use of the various kinds of words, to attempt the study of methods of philosophizing, would be as if some one should attempt to become an astronomical observer, having never learned to adjust the focal distance of his optical instruments so as to see distinctly.”
And here is Williamson’s way of putting a very similar point, in “Must Do Better“:
“Philosophers who refuse to bother about semantics, on the grounds that they want to study the non-linguistic world, not our talk about that world, resemble astronomers who refuse to bother about the theory of telescopes, on the grounds that they want to study the stars, not our observation of them. Such an attitude may be good enough for amateurs; applied to more advanced inquiries, it produces crude errors. Those metaphysicians who ignore language in order not to project it onto the world are the very ones most likely to fall into just that fallacy, because the validity of their reasoning depends on unexamined assumptions about the structure of the language in which they reason.”
Note that, despite the importance both place on questions of language, neither philosopher is adopting the position that philosophical inquiry is fundamentally inquiry about language. In fact, as revealed by the telescope analogy, both seem to be committed to the view that philosophical inquiry is often not about language.