understandable

comprehensible, conceivable, appreciable, expected, to be expected, natural, normal, regular, making sense, accordant, congruous, intelligible, coherent, lucid, unambiguous, in harmony with, readable, reasonable, logical, right, customary, recognizable, justifiable, imaginable, acceptable, apprehensible, credible, on all fours with*; see also obvious 2.

Antonyms illogical*, irrational, obscure.