Changes

If any evidence is found against a theory, and if the theory otherwise possesses both greater heuristic and explanatory powers than known alternatives, Lakatos supposed that falsification should be averted by modifying the research program's protective belt. There thus can be no 'crucial experiments'; a research program cannot be instantly overthrown by a single experimental finding taken in isolation.

new empirical content has been corroborated by experiments and observations, and if the modification is in organic unity with the rest of the program. A modification is deemed '''regressive'''if it does not increase the empirical content of a program by making novel predictions or improving its accuracy, or if it introduces excess empirical content, but fails to corroborate any of this excess content empirically, or if it is not in organic unity with the rest of the program. The term 'organic unity' is intended to mean that modifications should be contiguous with the rest of the program. For instance, if the research program is Darwin's theory of natural selection, a modification which adds the proposition “extra-terrestrial beings intervened with human evolution” would not be contiguous – not in organic unity – with the rest of the research program, and therefore regressive.