In philosophy, accidentalism denies the causal closure of physical determinism and maintains that events can succeed one another haphazardly or by chance (not in the mathematical but in the popular sense). Opponents of accidentalism maintain that what seems to be a chance occurrence is actually the result of one or more causes that remain unknown due only to a lack of investigation. Charles Sanders Peirce used the term tychism (from τύχη, chance) for theories that make chance an objective factor in the process of the Universe.