Materialism rest implicitly upon the general conception of nature promoted by Galileo and Newton during the seventeenth century. It features the causal closure of the physical: The course of physically described events for all time is fixed by laws that refer exclusively to the physically describeable features of nature, and initial conditions on these feature. No reference to subjective thoughts or feeling of human beings enter. That simple conception of nature was found during the first quarter of the twentieth century to be apparently incompatible with the empirical facts. The founders of quantum theory created a new fundamental physical theory, quantum theory, which introduced crucially into the causal structure certain conscious choices made by human agents about how they will act. These conscious human choices are free in the sense that they are not fixed by the known laws. But they can influence the course of physically described events. Thus the principle of the causal closure of the physical fails. Applications in psycho-neuro-dynamics are described.