Popper's criterion of Falsification does not take into account that Newtonian mechanics is not one single hypothesis, but a series of hypotheses that should be tested together. This is the main reason why Kitcher believes that Popper's criterion of Falsification is not adequate for distinguishing real science from pseudo-science.
In his book, Kitcher proposes a different criteria for separating science from pseudo-science. As opposed to Popper's single criterion, Kitcher presents three criteria. Independent testability, unification, and fecundity. Independent testability is achieved when the individual hypotheses of the theory is falsifiable. The hypotheses can be checked without having to make any assumptions. Kitcher uses the discovery of Neptune as an example to demonstrate this criterion. The existence of Neptune can be proved not only through the abnormal orbit of Uranus, it can be simply be proved by finding the actual planet itself using a telescope. Unification refers to the ability of a small number of problem-solving strategies to be applied to a large amount of varying situations. The example of Newtonian mechanics was used to demonstrate this condition. "Faced with any question about motion .tidal cycles and pendulum oscillations - all fell to the same problem-solving strategy." (P. 46-47). The final criterion is fecundity which basically states that a science should create more inquiries than it can resolve. "Because a theory presents a new way of looking at the world, it can lead us to ask new questions, and so to embark on new and fruitful lines of inquiry" (P. 48). .
Kitcher's criteria are highly successful because they take into account all the characteristics of a scientific theory and analyzes the amount of success the theory has in those individual categories. In his book, Kitcher evaluates Darwin's theory of evolution to see if it is science or pseudo-science. Kitcher first confirmed the unification of the theory.