He believes that the question of the nature of these changes is best asked by assuming that they were not used to create a more humanitarian penal system, nor to more exactly punish or rehabilitate, but as part of a continuing trajectory of subjection. Foucault wants to tie scientific knowledge and technological development to the development of the prison to prove this point. He defines a "micro-physics" of power, which is constituted by a power that is strategic and tactical rather than acquired, preserved or possessed. He explains that power and knowledge imply one another, as opposed to the common belief that knowledge exists independently of power relations (knowledge is always contextualized in a framework which makes it intelligible, so the humanizing discourse of psychiatry is an expression of the tactics of oppression). That is, the ground of the game of power is not won by "liberation", because liberation already exists as a facet of subjection. "The man described for us, whom we are invited to free, is already in himself the effect of a subjection much more profound than himself." The problem for Foucault is in some sense a theoretical modelling which posits a soul, an identity (the use of soul being fortunate since "identity" or "name" would not properly express the method of subjection—e.g., if mere materiality were used as a way of tracking individuals then the method of punishment would not have switched from torture to psychiatry) which allows a whole materiality of prison to develop. In "What is an Author?" Foucault also deals with notion of identity, and its use as a method of control, regulation, and tracking.