A principle used in the assessment of damages for breach of contract or tort. Losses may have been foreseeable at the time of contracting or at the time of the breach of duty in the case of tort, but they will only be recoverable if those losses were caused by the breach of contract or duty. The claimant must prove on a balance of probabilities that the breach caused the loss. It is not sufficient for the breach merely to provide the opportunity or occasion for the claimant to injure himself. The so-called “but for” test is used as a preliminary filter. If the loss would have happened in any event, then the breach could not be said to have caused the loss.