So if both mean “reason”, and the two of them together end up making the vocabulary for “reason”, 理由, what is the difference between them? Aside from their shape, of course.
Are they perhaps different kinds of “reason”, i.e. “reasoning / sense of reason” vs “the reason for x”?
This is fairly confusing, as if they are entirely the same, having two Kanji with different readings refer to the exact same concept seems… unreasonable.
From my understanding, the different kinds of reason are what the kanji mean on their own, but aren’t actual words. When you see them used in a word, this is the kind of meaning you can expect them to have in it, as with other Kanji.
理由, on the other hand, is the actual vocabulary for when you want to say the word “reason”.
In the example sentences for it, it is used for both cause and reasoning, so I’m guessing the vocabulary word works the same as the English “reason” does and encompasses both possible applications.