irrational — without the faculty of reason; deprived of reason.
obscure — (of meaning) not clear or plain; ambiguous, vague, or uncertain: an obscure sentence in the contract.
optional — left to one's choice; not required or mandatory: Formal dress is optional.
stupid — lacking ordinary quickness and keenness of mind; dull.
unclear — free from darkness, obscurity, or cloudiness; light: a clear day.
unintelligent — deficient in intelligence; dull; stupid.
unlikely — not likely to be or occur; improbable; marked by doubt.
unrealistic — interested in, concerned with, or based on what is real or practical: a realistic estimate of costs; a realistic planner.
unreasonable — not reasonable or rational; acting at variance with or contrary to reason; not guided by reason or sound judgment; irrational: an unreasonable person.
unsound — not sound; unhealthy, diseased, or disordered, as the body or mind.
unsuitable — not suitable; inappropriate; unfitting; unbecoming.
unwise — not wise; foolish; imprudent; lacking in good sense or judgment: an unwise choice; an unwise man.
vague — not clearly or explicitly stated or expressed: vague promises.
illogical — not logical; contrary to or disregardful of the rules of logic; unreasoning: an illogical reply.