Marx here criticizes the materialist philosophy of Ludwig Feuerbach for envisaging objects in a contemplative way. Marx argues that perception is itself a component of man's practical relationship to the world. To understand the world does not mean considering it from the outside, judging it morally or explaining it scientifically. Society cannot be changed by reformers who understand its needs, only by the revolutionary praxis of the mass whose interest coincides with that of society as a whole - the proletariat. This will be an act of society understanding itself, in which the subject changes the object by the very fact of understanding it.