The methodological roles of theory in science. In

Philosophy of science in this century can be roughly divided into two periods, positivist and postpositivist. Positivists maintained that scientific theories should be evaluated solely on the basis of observational data in accordance with a set of formal methodological rules. According to the positivists, both the data and the methodological rules are known independently of any scientific theories. Data are acquired by sense perception and they provide the empirical foundation for science. Methodological rules are established a priori and these rules provide a universal, permanent framework for the evaluation of scientific theories. One central postpositivist theme is that data and formal rules are not sufficient for evaluating scientific theories because they leave too many options open. Many different generalizations are compatible with any given body of data and, when an observation contradicts a theory, many responses remain possible. Postpositivists argue that, in scientific practice, these options are reduced because established theories take on a methodological role. These theories serve as guiding assumptions that, for a time, are not open to empirical challenge. Instead, thes