Linguistics is the scientific study of natural language. Semiotics, by contrast, is the scientific study of anything symbolic, whether natural language or not. For example, linguistics doesn’t study the artificial languages of logic and mathematics, but semiotics does.
What’s the significance of the distinction in linguistics between “natural language” and “artificial language?” What about the related distinctions between “children” and “adults,” “natives” and “foreigners”?
To think like a linguist is to bring a logical or mathematical mind to the analysis of “intuition,” the structure of natural language being isomorphic to the structure of “intuition.”
In practice, linguistics is often the scientific study of folk physics, folk psychology, etc.
In using phenomenalism to check whether we’re using language meaningfully, there’s the problem of how we can be said to mean so much more than we ever actually think. For example, how can we be said to mean the whole range of color associated with the word “black” even though, practically speaking, we’d only think of a handful of particular shades when saying the word?
The answer is that the meaning of a word (1) isn’t to be found only in what’s immediately present—only in what’s immediately introspectable due to being present to the “mind’s eye”—(2) nor is it to be found even in the aggregate of all that’s been present or introspectable to the individual across time; instead, (3) it’s to be found in the group—in the aggregate of all that’s been present or introspectable to all of the individuals involved across time. If a language evolves a word, then that word is presumably a common-enough indifference range. If one individual asks for “coffee,” and then another individual gives them something different than what they actually thought of, but they’re nevertheless no less satisfied, then neither individual will find any reason to change to using a different word.