> I'm only an armchair etymologist and this is wild speculation, but I think that the meaning of the "in" prefix might depend on whether we get the word directly from Latin, or whether it comes through French.
French has both meanings: the negation as in interdit (forbidden) or impossible (well, impossible); or “in”, “towards”, “change” as in intérieur (interior), inflexion (inflection), or indeed inflammable (from the Latin inflammabilis).
Both meanings also exist in Latin.
What I found fascinating learning English is “inhabit”, which also sounds like the opposite of its actual meaning. Is obviously the second meaning, but then the prefix is redundant because it came from the Latin habitare, which is the verb with the same meaning.
French has both meanings: the negation as in interdit (forbidden) or impossible (well, impossible); or “in”, “towards”, “change” as in intérieur (interior), inflexion (inflection), or indeed inflammable (from the Latin inflammabilis).
Both meanings also exist in Latin.
What I found fascinating learning English is “inhabit”, which also sounds like the opposite of its actual meaning. Is obviously the second meaning, but then the prefix is redundant because it came from the Latin habitare, which is the verb with the same meaning.
Anyway, that was today’s minute on etymology.