In many cases in natural language, causation must be treated as “defeasible”—that is, one event is asserted or presupposed to normally cause a second event, but there is no entailment that the second event actually occurs. To account for such cases, we propose that the arguments discovered by Davidson refer to forces instead of to events. A force, conceptually, is energy input into a situation. Formally, we treat forces as functions from an initial situation to the situation that results ceteris paribus (all else being equal). This allows for the possibility that all else may not be equal, leading to the lack of a causative entailment. The key feature of the approach is that it allows a simple semantic characterization of a ‘normal’ result that does not entail the existence of that result; in standard event-based treatments, in contrast, possible words or partial events are needed to defeat this entailment; the adoption of possible worlds over-complicates the semantics while the use of partial events glosses over the issue of how to link causes and results. We illustrate the framework with an analysis of the frustrative morpheme cem in Tohono O’odham, a Uto-Aztecan language spoken in southern Arizona and northern Mexico. The resulting analysis sheds light on statives, plans, and prospective, imperfective, and perfective aspect.