Assault or criminal force not on grave provocation attracts punishment; exceptions invalidate provocation and factual inquiry required. Section 131 establishes that assault or criminal force committed otherwise than on grave and sudden provocation is punishable. Mitigation by provocation is excluded if the provocation was sought or voluntarily provoked by the offender, if it arose from acts done in obedience to the law or by a public servant lawfully exercising powers, or if it resulted from the lawful exercise of the right of private defence. Whether provocation was grave and sudden enough to mitigate is a question of fact.