Changes

Following the Quine-Duhem thesis, Lakatos recognized that scientific theories could not be appraised individually. Rather, all of the theoretical assumptions bearing on an experimental finding had to be assessed holistically. Lakatos proposed that not all theoretical assumptions are treated equally. Instead, scientists adhere to research programs. A research program consists of a "hard core" of theoretical assumptions, which are its indispensable constituents. Any modification of the "hard core" results in the creation of a new research program. Adherents of a research program attempt to explain an increasingly wide range of relevant natural phenomena in terms of the core. In so doing, they create a "protective belt" of auxiliary propositions. This expansion of the range of applicability of the program constitutes its "positive heuristic". Scientists committed to a research program defend the "hard core" against change by using their ingenuity as needed to make alterations to the "protective belt" of auxiliary propositions to explain phenomena and avoid falsification of the core. This protection of the hard core is a research program's "negative heuristic". For example, the "hard core" of the Newtonian physics research program would consist of Newton's three laws of motion and Law of Universal Gravitation. The protective belt would include propositions such as "the Earth is an oblate spheroid" or "Neptune is 17 times more massive than Earth". In the nineteenth century, astronomers could not explain the movements of the planet Uranus using Newton's theory and known gravitational influences. Rather than modifying the theory itself, which would have obviated the Newtonian research program, they modified the protective belt by positing the existence of a new planet, whose Newtonian gravitational influence was affecting Uranus. The prediction was a stunning success, as the new planet, to be named Neptune, was discovered in 1846<ref>Chalmers, A. F. 2013. What is This Thing Called Science? Hackett Publishing.</ref><ref>Lakatos, I. 1978 The Methodology of Scientific Research Programmes, Philosophical Papers: Volume 1, Edited by J. Worrall and G. Currie, Cambridge: Cambridge University Press</ref><ref>Solar System Exploration, National Aeronautics and Space Administration, Neptune: In Depth, http://solarsystem.nasa.gov/planets/neptune/indepth</ref>.

Lakatos held that a research programme should be chosen for both its “explanatory power” and its “heuristic power”. That is to say that a theory is accepted for its ability to both explain past and present phenomena, as well as its ability to be applied to and posit the existence of future phenomena and anomalies. Given any evidence against a theory, if the theory possesses both greater heuristic and explanatory powers than its counterparts, its protective belt should be allowed to undergo modifications and avoid falsification. These modifications should be “progressive” and intended to save the research programme from degenerating. This, for Lakatos, represents the difference between falsification and rejection.

A research programme is considered “progressive” if it can make predictions later confirmed by experiment, much in line with the Popperian notion of “novel predictions”. On the other hand, if a theory fails to offer such predictions and merely attempts to “save” itself from a disproving instance, it is considered “degenerative”. Lakatos established the following criteria for appraising modifications: