Causation

The accepted wisdom on 'causation' was, and mostly is, the 'but for' standard. It stems from the philosophy that delineates 'necessary' and 'sufficient' causes. A 'necessary' cause is one that amongst others has to be present for the effect to take place, and a 'sufficient' cause is one that by itself can create the effect. A 'but for' cause is a human-created necessary cause.

Mind you, with law being a thoroughly social activity, with social mores at it heart, it's not always quite so simple. Even when not dealing with 'proximate cause' (with the added legal policy issues of remoteness, proximity and more) causation is inherently a social creation, not a feature of physics. Causation can often be a complex and uncertain matter.

General

'But for' and Complications
Significant Contributing Cause
Break in Chain of Causation (Novus Actus Interveniens)
Modified Objective Causation
Burden of Proof
Loss of Chance