A criminal-law concept describing conduct, procedure, or legal consequence defined by governing offense or rule elements. It applies only when the legally specified conditions for its use or enforcement are satisfied. It does not apply where required elements or conditions are absent. It materially affects charging, adjudication, detention, or sanction decisions in practice. The concept is generally stable, though elements and penalties may be revised over time.

Principle

But-for causation identifies necessary links in the causal chain by applying a counterfactual: remove the defendant’s act and ask whether the result still happens; it establishes factual necessity but not necessarily legal responsibility in complex cases.

Demonstration

If a driver stabs a pedestrian and the victim dies from those wounds, a but-for test asks whether the death would have occurred without the stabbing; if not, the stabbing is a but-for cause of death.

Misapplication

Using the but-for test where multiple independent sufficient causes exist (overdetermination) or where intervening acts break the causal link, leading to incorrect attribution of causation when no single cause is necessary.

Consequence

But-for causation narrows the field of potential causes to those without which the harm would not have occurred, clarifying which actions are candidates for legal responsibility before normative proximate-cause analysis is applied.

Reversal

Treating but-for causation as sufficient alone for legal liability in every case, thereby ignoring intervening acts, foreseeability, and policy limits that may absolve a defendant despite factual necessity.

Boundary

Operates at the level of factual necessity and is often the first causation step; it fails in cases of concurrent sufficient causes, complex causation chains, or omissions that require special treatment and must be supplemented by normative causation doctrines.

Semantic Tension

Tension with proximate and legal causation doctrines: but-for test is crisp and fact-focused but can produce counterintuitive results when multiple sufficient causes or long causal chains exist, requiring doctrinal refinement.

Synthesis

But-for causation is the initial counterfactual screen that isolates necessary factual causes—those without which the harm would not have occurred—forming the empirical core that normative proximate-cause rules then constrain.