illogical

Synonyms: absurd casuistic cockeyed fallacious false fatuous faulty groundless hollow implausible inconclusive incongruous inconsequent inconsistent incorrect invalid irrational irrelevant mad meaningless not following nutty off the wall preposterous screwy self-contradictory senseless sophistic sophistical specious spurious unconnected unproved unreasonable unscientific unsound unsubstantial untenable wacky without basis without foundation

Antonyms: correct logical meaningful rational reasonable right sensible