v York Montague Ltd gave a classic example. "A mountaineer about to undertake a difficult climb is concerned about the fitness of his knee. He goes to a doctor who negligently makes a superficial examination and pronounces the knee fit. The climber goes on the expedition, which he would not have undertaken if the doctor had told him the true state of his knee. He suffers an injury which is an entirely foreseeable consequence of mountaineering but has nothing to do with his knee." The doctor's negligence does result in the mountaineer running a risk which he otherwise would not have done, but this is insufficient to incur liability. The purpose of the doctor's duty to take care is to protect the mountaineer against injuries caused by the failure of the knee, not rock falls. Even though the injury might be reasonably foreseeable, the doctor is not liable. In The Empire Jamaica (1955) 1 AER 452, the owners sent their ship to sea without properly licensed officers. The pilot fell asleep, and a collision occurred. Though the pilot was negligent at the time, he was generally competent. Thus the question for the courts was: were the owners liable for the collision because they sent their ship to sea without properly licensed officers? Or was the factual precondition superseded by the question as to the competence of the pilot? There is no question that sending the ship to sea is "a cause" of the collision. The legal question is whether it is "the cause". This is a question that the courts treat as objective, addressed by evidence and argument. Hart and Honoré (1985) describe the process for establishing legal causation as constructing a parallel series of events (counterfactual situation), and comment: "the parallel series is constructed by asking what the course of events would have been had the defendant acted lawfully." Thus, the owners were not liable. Although they sent the ship to sea without licensed officers (what actually transpired) rather than with licensed officers (the lawful course), the cause of collision was failing to navigate a safe passage. As to the pilot, his lack of licence did not bear on his general competence. The significant factor was the pilot's negligence at the time, and the pilot's lack of license made no difference there. Had the pilot been licensed, he would have been no less likely to sleep. The license would