Synonyms of illogical

1 Syllable

mad

2 Syllables

wacky, silly, sappier, sillier, groundless, screwy, fatuous, madder, nutty, faulty, maddest, absurd, cockeyed, spurious, sappy, unsound, specious, silliest, false, hollow

3 Syllables

casuistic, birdbrained, incorrect, mistaken, sophistic, inanest, fallacious, meaningless, ill-founded, invalid, incongruous, unbacked, unproved, senseless, inane, far-fetched, unfounded, farfetched, obscurer, nonviable, reasonless

4 Syllables

unscientific, implausible, irrelevant, unthinkable, irrational, muddleheaded, untenable, preposterous, disconsonant, inconsequent, impractical, unsubstantial, disconnected, unconnected, sophistical, scatterbrained, infeasible, unreasoned, inconsistent

5 Syllables

unreasonable, unnegotiable, inconclusive, unserviceable

6 Syllables

self-contradictory, counterintuitive, unbusinesslike