Positivistic social sciences are concerned with developing verifiable knowledge. The logical positivists of the Vienna Circle developed the verifiability principle of meaning which contended that something is meaningful only if it is verified through the senses (empirically). The verifiability principle necessitates the use of operational definitions to specify that which is under study (Popkewitz, 1981b; Phillips, 1983). An operational definition assigns meaning to an entity by enumerating the activities (operations) necessary to its measurement. The operational definition serves as a manual of instructions for a researcher, granting him or her a list of activities necessary to the research process. Fred Kerlinger gives an example of an operational definition of intelligence: 'Intelligence…is scores on X intelligence test, or intelligence is what X intelligence test measures' (Kerlinger, 1973:31).
The positivistic impulse and the behaviorist research traditions merge with Thorndike's argument that anything which exists, exists in some amount and can thus be measured. Such an idea when applied to education focuses research on statistical analysis of quantified variables. If the objects of positivistic research in education can always be quantified, then antipositivists argue that quantifiability becomes an essential precondition for that which is to be studied. Thus, given enough time the truth or falsity of the findings of educational research can be established-that is, data can ultimately be verified in a quantifiable manner (Macmillan and Garrison, 1984; Donmoyer, 1985; Lather, 1991).
Denis Phillips (1983) claims that the verifiability principle of the logical positivists died long ago, choked to death under its own weight. It was never clear about how to verify scientific principles-using its own criteria for meaning, a principle was not verifiable through the senses. Instead of criticizing and misrepresenting positivism, Phillips argues, eclecticists such as Eisner and Giroux should begin devising methods of verifying knowledge and separating fact from belief.