 Philosophers draw a distinction between strict generalizations and ceteris-paribus generalizations. The contrast is supposed to be between universal generalizations of the sort discussed above (e.g., that all inertial bodies have no acceleration) and seemingly less formal generalizations like that, other things being equal, smoking causes cancer. The idea is that the former would be contradicted by a single counterinstance, say, one accelerating inertial body, though the latter is consistent with there being one smoker who never gets cancer. Though in theory this distinction is easy enough to understand, in practice it is often difficult to distinguish strict from ceteris-paribus generalizations. This is because many philosophers think that many utterances which include no explicit ceteris-paribus clause implicitly do include such a clause.