Where there's Smoke there's Fire
Non fumum ex fulgore, sed ex fumo dare lucem cogitat.
WE STARTED OUT with the question: Does smoking cause cancer ? Prosecution and defence have both had their say; what is the verdict? Clearly the accused does not emerge with an untarnished reputation. Studies of the lungs of smokers and non-smokers reveal deleterious after-effects very clearly among the former; dangerous substances are precipitated in the lungs, and the ciliary movements by means of which these substances are normally removed are themselves impeded by smoke. Some of these substances, such as the cyclic hydrocarbons and some radioactive isotopes of polonium, are known to or suspected of producing cancerous growths. Clearly, smoking is not likely to promote anyone's health, and suspicion is very strong that cigarette smoking may indeed be a killer. However, in science as in law, the accused is presumed innocent unless proven guilty, and it must be said that the evidence, although strong, is not conclusive; it is circumstantial rather than direct, and it does not demonstrate the case against smoking 'beyond any reasonable doubt'. This conclusion of 'not proven' must, of course, leave open the question of just how reasonable doubt is at this juncture; we have pointed out that scientific evidence is never 'certain' in the philosophical meaning of that term, and that different people have different psychological thresholds of 'certainty' which will determine what they are prepared to regard as 'reasonable' in the way of doubt.