Empirical knowledge includes physics, biology, psychology, etc. If they were, with respect to time, at the beginning of the knowledge, then they would be logically useless. Obviously if and only if we are able to exactly describe the conditions in which it is possible to answer yes, or, respectively, the conditions in which it is necessary to answer with a no. The definition of the circumstances under which a statement is true is perfectly equivalent to the definition of its meaning. The only role of philosophy is the clarification of the meaning of statements and their logical interrelationships.
Philosophy is the activity by means of which the meaning of statements is clarified and defined.
This conception about the structure of scientific theories is perhaps the most durable philosophical principle of the logical positivism. These four points are linked together. Rules of correspondence give an empirical meaning to theoretical terms and are analytic, while theoretical axioms express the observational portion of the theory and are synthetic. The distinction between observational and theoretical terms depends on the verifiability criterion of meaning. The theoretical terms which belong to the abstract language of a scientific theory are explicitly definable in a restricted language whose terms describe only that which is directly observable.