はずがない

はずがない is used when the speaker is certain that something cannot be the case, often because of strong evidence, expectations, or common sense. It conveys a firm denial of a situation that would be surprising or unacceptable if true. It can sound confident or even blunt, so use in casual or familiar contexts, and with care in formal settings. Typical contexts: denying someone’s claim, rejecting a possibility you know is false, or reacting to something that was rumored but you are sure it’s not true. Do not use for mere guesses or probabilities; use when you are sure and want to emphasize the impossibility.