“Fact” as a concept developed in the early Enlightenment era of the 17th century, when scientists began to assume that an observer can confront scientific phenomena “face-to-face without any theoretical interpretation” (79)—which MacIntyre describes as “an error” and one recognized as such by modern scientists. However, the idea of “fact” led to the development of empiricism in philosophy, based on observed experience, and to the “conceit” that modern (i.e., Enlightenment) thinkers had freed themselves from “interpretation and theory,” especially as embodied in Aristotle’s thought, and could now see things plainly as they really were.

This in turn led to a new distinction between “facts” and “values” and between morality and science which was unknown in the Aristotelian system. Explaining mechanical processes began to take precedence over explaining action in terms of ends or purposes, with human actions in particular being disassociated from any consideration of “good or virtue.” The result of this change is, MacIntyre writes, a “divorce between ‘is’ and ‘ought’” (84).

The new mechanistic science of human behavior opened the door to the possibility of scientists manipulating human behavior for the sake of influencing nature or society, and then treating this activity as an exercise of their “rational autonomy.