Any system of thought that denies the causal nexus and maintains that events succeed one another haphazardly or by chance (not in the mathematical but in the popular sense). In metaphysics, accidentalism denies the doctrine that everything occurs or results from a definite cause. In this connexion it is synonymous with tychism (ruxi, chance), a term used by Charles Sanders Peirce for the theories that make chance an objective factor in the process of the Universe.