why do we need to study english?

Yeah see I thought full and free were untenable until I thought up "Keep (the car's gas tank) full" (because it's less efficient when it's getting close to empty) and "Keep (your Saturdays) free" (because there's something which is liable to use that timeslot).

There's something disquieting about looking at a sentence like "You can eat rice every day to keep your health" and knowing it's wrong but not being able to explain why.

(My logic went "you can only use "keep" to verb several specific nouns, like animals or habits" > "you can use "keep" on some adjectives, but some arbitrarily sound weird" > "It's about intent? Maybe? It sounds weird unless you're actively doing something, for a logical reason")