Today we cover the transition from the young Marx, with his emphasis on change and action, to the mature Marx who turns toward positivist science and determinism, arguing that capitalism will have to fail. Through a closer look at Marx's "Theses on Feuerbach," we discuss different theories of truth with attention to the questions of where truth resides (in the subject, in the object, or some combination), how we know it, and how we know when we know it. Arguing for his conception of materialism, Marx argues that truth is not simply the reflection of the object in the mind of the subject; we must access truth through our senses and through activity. And we discuss two of Marx's historical materialist claims: life determines consciousness and the ruling class always determines the ruling ideas of a people.