32 SOCIAL SCIENTIST philosophy of psychology. And it is to this problem the famous incommensurability thesis is related. The history of science is full of theory transitions or replacements, like Aristotelian cosmology to Copemican cosmology, Galilean physics to Newtonian physics, overthrow of the phlogiston theory, and the replacement of Newtonian physics with the special and general theory of relativity, etc. The reflection on such theory replacements or changes warrants us to study the nature of the relation between successive scientific theories. The problem of theory change can be discussed under the following four related and over-lapping issues. 1. Connection : How are^sucessive scientific theories connected ? Or how can we establish relationship between them ? 2. Comparability And Translatability : How can we compare the successive scientific theories ? Or are there any unchanging, universal standards of reasoning or criteria of rationality to compare them ? Or if all standards of reasoning or criteria of rationality are subject lo change then how can we compare the successive theories of science ? 3. Rationality : How could criteria of rationality themselves be said to evolve rationally, unless there are higher level standards or criteria of rationality themselves immune to alteration, in terms of which changes of lower-level criteria of rationality could be judged to be rational ? 4. Progress : Is scientific activity a progressive activity ? Or if successive theories are incommensurable then how can we say that science is progressing ? The discourse among the philosophers of science on these issues of theory change has been taking very fascinating and serious turn since the demise of empiricist model of explanation. The outstanding representatives of philosophy of science have been taking different ideological stands and orientations in constructing their theories about scientific change and its related issues. This ideological polarization in philosophy of science gave rise to conflicting and contrasting views about the fundamental notions of science like, rationality, objectivity, logicality, problem-solving, discovery-justification relation, evaluation, scientific progress, and also the growth and evolution of scientific knowledge. This debate has been manifesting in the form of rationalist-non-rationali^t-and-irrationalist dispute and as realism-and-non-realism controversy. Contemporary philosophies of science have addressed themselves to the above mentioned issues and inspite of the fundamental differences between them have shed considerable light on the problem of theory change bv putting forward their models of scientific change like Deductive model. Gestalt model, Perspectivist conception of science, Set-theoretic conception of science, etc. However, in the present literature of philosophy of