Paul Thagard

“The question about comparing the success of a theory with that of other theories introduces the third element of the matrix, historical context; The historical work of Kuhn and others has shown that in general a theory is rejected only when (1) it has faced anomalies over a long period of time and (2) it has been challenged by another theory. Hence under the heading of historical context we must consider two factors relevant to demarcation: the record of a theory over time in explaining new facts and dealing with anomalies, and the availability of alternative theories.
We can now propose the following principle of demarcation:
A theory or discipline which purports to be scientific is pseudoscientific if and only if:
1. it has been less progressive than alternative theories over a long period of time, and faces many unsolved problems; but
2. the community of practitioners makes litde attempt to develop the theory towards solutions of the problems, shows no concern for attempts to evaluate the theory in relation to others, and is selective in considering confirmations and disconfirmations.
Progressiveness is a matter of the success of the theory in adding to its set of facts explained and problems solved.”
― Paul Thagard