 While the argument from analogy was once popular in science (Hyslop &amp; Jackson (1972) cite the example of the discovery of helium on the sun to have a characteristic spectrum by analogy with the characteristic spectrum of helium on earth) in more recent times science has tended to proceed in accordance with the principle that it is rational to believe that hypothesis that provides the best available explanation of a particular phenomenon at a given time. This style of argument is sometimes referred to as abduction, and it is placed alongside deduction and enumerative induction as another form of inferential reasoning. While simple enumerative inductive takes one from certain observations to the conclusion that one can expect more of the same, abduction allows for the introduction of entities that are not just unobserved, but that are unobservable (Lipton 2000; Harman 1965).