Positivism is a philosophical theory that holds that all genuine knowledge is either positive—a posteriori and exclusively derived from experience of natural phenomena and their properties and relations—or true by definition, that is, analytic and tautological. Thus, information derived from sensory experience, as interpreted through reason and logic, forms the exclusive source of all certain knowledge.
Verified data (positive facts) received from the senses are known as empirical evidence; thus positivism is based on empiricism.
Sociological positivism holds that society, like the physical world, operates according to general laws. Introspective and intuitive knowledge is rejected, as are metaphysics and theology because metaphysical and theological claims cannot be verified by sense experience. Although the positivist approach has been a recurrent theme in the history of western thought, the modern approach was formulated by the philosopher Auguste Comte in the early 19th century. Comte argued that, much as the physical world operates according to gravity and other absolute laws, so does society.
Logical positivism is a branch of philosophy that requires that certainty or truth has two alternative tests: (1) It is by definition so, e.g. 2+3=5 is true; (2) it can be independently verified by external observation to be so, e.g. you are reading this text at this moment. Anything else is logically meaningless, e.g. the statement "God exists".