hard to believe

ambiguous arguable controversial debatable dubious problematic suspicious unproven vague

apocryphal contingent controvertible cryptic disputable dubitable enigmatic equivocal fishy hypothetical iffy indecisive indefinite indeterminate moot mysterious obscure occult open to doubt open to question oracular paradoxical problematical provisional shady suspect unconfirmed undefined under advisement under examination unreliable unsettled

certain clear definite incontrovertible indubious sure trustworthy trusty undoubted unquestionable

indisputable proven

debatable dubious unsupported

arguable controversial disputable doubtful dubitable fishy iffy indefinite open to doubt open to question suspect suspicious uncertain unconfirmed uncorroborated

certain sure