 Like Kuhn’s paradigms and Laudan’s research traditions (see below), the unit of rational appraisal for Lakatos is not a single theory at a point in time; instead, it is a series of theories that are rationally-connected moments in the development of an identifiable research program. In MSRP these theories share a negative heuristic containing inviolable principles and a positive heuristic that both provides a “protective belt” around the negative heuristic and guides future research. The forward-looking heuristic element was, as for Kuhn, an important feature missing from traditional accounts of science. In MSRP, research programs are evaluated as to their progressiveness over historical time, i.e., which grows knowledge fastest. Lakatos’s measure of knowledge growth is novel prediction, the advantage going to which program yields more novel theoretical predictions and more confirmed novel predictions than its competitors. This is a historicist position since determining whether something is a novel prediction requires detailed knowledge of the historical context of discovery in which the predictive theory was produced (Lakatos &amp; Zahar 1976). Unfortunately, however, Lakatos’s falsificationism had become so sophisticated that he could provide no rule for when it was rational to abandon a degenerating research program that was being outstripped by a more progressive one; for scientists, he said, may legitimately make risky choices. In any case, contrary to Kuhn, two or more research programs may exist side-by-side. Lakatosian rationality does not dictate that researchers all join the same program.