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".
The development of contemporary civilization is linked to a scientific and technological progress which is often achieved in a one-sided way, and thus appears purely positivistic. Positivism, as we know, results in agnosticism in theory and utilitarianism in practice and in ethics. (Pontifical Council for the Family: The Truth and Meaning of Human Sexuality, 1995).
In the field of scientific research, a positivistic mentality took hold which not only abandoned the Christian vision of the world, but more especially rejected every appeal to a metaphysical or moral vision. It follows that certain scientists, lacking any ethical point of reference, are in danger of putting at the centre of their concerns something other than the human person and the entirety of the person's life. Further still, some of these, sensing the opportunities of technological progress, seem to succumb not only to a market-based logic, but also to the temptation of a quasi-divine power over nature and even over the human being. As a result of the crisis of rationalism, what has appeared finally is nihilism. As a philosophy of nothingness, it has a certain attraction for people of our time. Its adherents claim that the search is an end in itself, without any hope or possibility of ever attaining the goal of truth. In the nihilist interpretation, life is no more than an occasion for sensations and experiences in which the ephemeral has pride of place. Nihilism is at the root of the widespread mentality which claims that a definitive commitment should no longer be made, because everything is fleeting and provisional. (Papal Encyclical, Fides et Ratio, 14 September 1998).