Assumption of risk historically operated as a single, often complete, defense: a plaintiff who voluntarily encountered a known risk could not recover at all. The adoption of comparative negligence in most jurisdictions forced courts to reexamine that all-or-nothing rule, and the resulting doctrine split into two conceptually distinct branches that behave very differently at trial.

Primary assumption of risk is really a statement about the defendant's duty, not about the plaintiff's fault: for risks inherent in certain activities, courts hold the defendant simply never owed a duty to protect the plaintiff against that inherent risk in the first place, so there is no negligence to compare and the claim fails as a matter of law. Secondary assumption of risk, by contrast, presupposes the defendant did owe and breach a duty, and asks only whether the plaintiff knowingly and voluntarily encountered the resulting risk anyway, a question most comparative-fault jurisdictions now fold into the ordinary allocation of fault rather than treating as a complete bar.

Primary assumption of risk typically arises in the context of sports, recreational activities, and other pursuits with risks inherent to the activity itself, that cannot be eliminated without fundamentally changing the nature of the activity, such as the risk of being struck by a ball at a sporting event or the risk of falling while skiing. Under this branch, the defendant (often a co-participant, coach, or venue operator) owes no duty to protect participants and spectators against those inherent risks, though a duty still exists not to increase the risk beyond what is inherent to the activity, for example through reckless or intentional conduct unrelated to normal play.

Secondary assumption of risk covers situations where the defendant did owe and breach an ordinary duty of care, but the plaintiff nonetheless voluntarily and knowingly chose to encounter the resulting risk, such as riding as a passenger with a driver known to be impaired, or continuing to work with equipment known to be defective. It can be express, arising from an explicit agreement or waiver, or implied, inferred from the plaintiff's conduct and knowledge. In the large majority of jurisdictions that have adopted comparative negligence, implied secondary assumption of risk is no longer a complete bar to recovery; instead it is treated as a form of comparative fault, reducing the plaintiff's recovery in proportion to the reasonableness of encountering the known risk, while express assumption of risk (a valid waiver) often remains a complete defense where enforceable.

Because primary assumption of risk eliminates the duty element itself, it remains a complete defense even in pure comparative-fault jurisdictions, since there is no breach to allocate fault against. Secondary assumption of risk survives comparative-fault reform in a fundamentally changed form: it no longer operates as an independent, freestanding bar in most jurisdictions, but is instead absorbed into the same fault-allocation analysis as ordinary contributory negligence, which is why courts and litigants must first correctly classify a case as primary or secondary before they can know whether the doctrine can end the case outright or merely shifts a percentage of the damages.

Juricratic models primary assumption of risk as a threshold duty-gate dial: when set to apply, it can zero out the underlying negligence claim entirely regardless of how the other elements are scored, reflecting that no breach analysis is ever reached. Secondary assumption of risk, by contrast, is modeled downstream as a comparative-fault input that shifts the damages allocation dial rather than gating the claim itself. Running both configurations on the same fact pattern lets a user see, as a simulation artifact, how misclassifying a case's assumption-of-risk theory can be the difference between a complete defense and a modest damages offset.