Causal Generalizations and Good Advice

[Introduction] The aim of this paper is to explicate causal generalizations such as: G: Smoking causes lung cancer. Such generalizations are relatively unproblematic when applied to a homogeneous population. The problem takes on an added layer of complexity when G is asserted of a heterogeneous population. Perhaps some individuals in the population are protected from the harmful effects of smoking; perhaps some are such that smoking even reduces the risk of lung cancer. Just how many such individuals can there be in a population before G ceases to accurately characterize it?