" Certain kinds of theory -- emancipatory theories, as they are generally known -- can act as a political force within the world, not just as a way of interpreting it. And this lends them a peculiar sort of feature. It means that they form a link between how things are and how they might be. They provide descriptions of how the world is; but in doing so they can help change the way men and women understand it, which in turn can play a part in changing reality. A slave knows he is a slave, but knowing why he is a slave is the first step towards not being one. So in portraying things as they are, such theories also offer a way of moving beyond them to a more desirable state of affairs. They step from how it is with them to how it ought to be. Theories of this kind allow men and women to describe themselves and their situations in ways that put them into question, and therefore eventually allow them to redescribe themselves. In this sense, there is a close relationship between reason, knowledge and freedom. Certain kinds of knowledge are vital for human freedom and happiness. And as people act on such knowledge, they come to grasp it more deeply, which then allows them to act on it more effectively. The more we can understand, the more we can do; but in Marx's view the kind of understanding that really matters can come about only through practical struggle. "

― Terry Eagleton , Why Marx Was Right