But-For Test

The ‘but for’ test asks a counterfactual question: strip out the defendant's wrongdoing, and ask whether the claimant's or victim's harm would still have occurred. CPS legal guidance on corporate manslaughter applies exactly this formulation to failures by omission, directing that “The prosecution must prove that, but for the alleged gross breach of duty, the deceased would have survived”, or would not have died at that time or in those circumstances — if the outcome would have been the same regardless of the breach, factual causation fails.

Applying the test is not always a single, simple comparison. Where a case relies on a series of failings across a period of time rather than one discrete omission, the same CPS guidance recognises that “the question of whether the deceased would have survived but for the gross breach of duty may require very careful analysis of the timeline” to identify when the breach was operative and whether earlier intervention would have changed the outcome. The same counterfactual approach to factual causation is applied across both the criminal law and the civil law of negligence.