From Latin 'asserere' — originally the legal act of claiming a slave's freedom, making assertion's origin an act of liberation, not mere declaration.
To state a fact or belief confidently and forcefully; to exercise or defend a right or claim.
From Latin assertus, past participle of asserere (to claim, to maintain, to free a slave), composed of ad- (to, toward) + serere (to join, to bind, to connect in a series), from PIE *ser- (to line up, to join in sequence). In Roman law, asserere in libertatem meant physically laying a hand on an enslaved person and claiming them as free before a magistrate — a gesture of joining someone to liberty. The PIE root *ser- also produced series, sermon (words joined together