irrational

Synonyms: aberrant absurd brainless cockamamie crazy delirious demented disconnected disjointed distraught fallacious flaky foolish freaky incoherent injudicious insane invalid kooky loony mad mindless nonsensical nutty off-the-wall preposterous raving reasonless ridiculous silly sophistic specious stupid unreasonable unreasoning unsound unstable unthinking unwise wacky wild wrong

Antonyms: logical rational reasonable reflective sensible sound stable