This article is about the dispute between existentialism and physicalism concerning the in/authenticity of the human being's thought and freedom. It deals with the impossibility of reducing human thought, practice, choice, and decision to their physical, biological, brain-based or neurological aspects. In other words, the way of thinking which can be called naturalism, materialism, or physicalism based on different criteria (from seventeenth-century until twentieth century) tries to interpret human existence (“soul” in the mythological language of Plato, “transcendental imagination” in Kant’s (...) philosophy, “existence” in Kierkegaard’s thought and existentialism and “_Dasein_” in Heidegger’s view) as a product of physical, natural or material processes and does not regard human freedom of choice as authentic (or irreducible) but as a secondary product of biological natural phenomena. This article claims that the main matter of the dispute is not specifically determined in the debate between physicalism or reductionism on the one hand and the philosophers believing in existence or Dasein on the other hand. This vagueness has caused the discussion about the theoretical challenge not to undergo a smooth path. In order to make clear the exact parameters of the central matter of dispute, I try to challenge the fundamentals of physicalism. (shrink)