A controversial philosophical position that everything that has happened must have necessarily happened due to prior conditions, and that chance is a merely a measure of human ignorance. By studying causality, it's easy to see that certain causes always produce certain effects; as to why this happens, it's not entirely clear why this is (per David Hume). Kant and Schopenhauer had worthy responses to this mystery.
An antithesis to determinism is the theory of free will. My chief argument against free will and for determinism is a simple one: while it's easy to describe what determinism is and theorize about states of affairs in deterministic systems, descriptions of the nature of free will is always unsatisfactory. The system of free will is ultimately religious in nature: we have agency, good and bad actions are the result of someone's “free” decision making, and thus that soul is sent to heaven or hell (or rewarded with good or bad karma) as a consequence.
If we understand that the myth of free will is a noble lie meant to encourage good behavior, I contend (as a determinist) that belief in free will and metaphysical consequences is likely to improve the conduct of individuals and bodies. However, we do not need to accept “free will” to justify consequences. We can still punish a murderer the way we put down a rabid dog or put out a blazing fire. Regardless of whether a good or bad action is the result of a soul, the individual is ultimately the owner of their actions and behaviors, and we should respond accordingly.