Positivism is a philosophical theory stating that certain ("positive") knowledge is based on natural phenomena and their properties and relations. Thus, information derived from sensory experience, interpreted through reason and logic, forms the exclusive source of all certain knowledge. Positivism holds that valid knowledge (certitude or truth) is found only in this a posteriori knowledge.
Verified data (positive facts) received from the senses are known as empirical evidence; thus positivism is based on empiricism.
Positivism also 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".