Critical theorists argue that in the ancient world the concept of ‘reason’ was an objective and normative one. Reason was thought to refer to a structure or order of what ought to be which was inherent in reality itself and which prescribed a certain way of life as objectively rational. Human beings were thought to have a (subjective) faculty which allowed them to perceive and respond to this objective structure of the world; this faculty could then also be called reason in a derivative sense. Even when ancient philosophers spoke of reason as a human faculty (rather than as a structure of the world), their conception of it was ‘substantive’; humans were thought to be able to use reason to determine which goals or ends of human action were worthy of pursuit.

In the post-Enlightenment world the ‘objective’ conception of reason becomes increasingly implausible. Reason comes to be conceived as essentially a subjective ability to find efficient means to arbitrarily given ends; that is, to whatever ends the agent in question happens to have. The very idea that there could be inherently rational ends is abandoned. Reason becomes subjective, formal and instrumental.

The historical process by which reason is instrumentalized is in some sense inevitable and irreversible. The philosophical position called ‘positivism’ draws from this the conclusion that reason itself should simply be identified with the kind of reason used in natural science. Scientific reason, the critical theorists claim, is a particularly highly developed form of instrumental reason. The point of getting an exact depiction of reality as it is and of the causal laws that govern events is to allow humans to manipulate the world successfully so as to attain their ends. — Routledge Encyclopedia of Philosophy, Critical Theory

mechanized — Pneumenon