There may well be as much controversy surrounding Marx's theory of knowledge and related phenomena such as ideology as there is about his views on human nature more generally. Did Marx reject "the classical definition of truth" and replace it with a conception of truth about reality, indeed, of reality itself, as constructed and proven in the process of modifying nature through praxis? Are individuals' observation and experience of reality direct or immediate, as philosophical "empiricists' have usually claimed, or only mediated through collective and individual praxes? If the latter is the case, what are these praxes and precisely how do they relate to individuals' knowledge?