Karl Marx wrote the “Theses on Feuerbach” in Brussels, in the spring of 1845, when he had already finished developing the main features of his materialist theory of history and had extended materialism to the explanation of human society. According to Engels definition, it is “… the first document in which the initial germ of the new conception of the world is contained”.
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1. The fundamental flaw of all previous materialism – including that of Feuerbach – is that it conceives only things, reality, sensoriness, in the form of object or contemplation, but not as a human sensory activity, not as a practice, not in a subjective way. Hence, the active side was developed by idealism, as opposed to materialism, but only in an abstract way, since idealism, naturally, does not know real, sensory activity as such. Feuerbach wants sensory objects, really different from conceptual objects; but neither does he conceive of human activity itself as an objective activity. That is why, in The Essence of Christianity, he only considers the theoretical attitude as authentically human, whereas he conceives and fixes the practice only in its filthy Jewish form of manifestation. Therefore, it does not understand the importance of “revolutionary”, “practical-critical” action.

2. The problem of whether human thought can be attributed an objective truth, is not a theoretical problem, but a practical problem. It is in practice that man has to demonstrate the truth, that is, reality and power, the earthiness of his thought. The litigation about the reality or unreality of a thought that is isolated from the practice, is a purely scholastic problem.

3. The materialist theory that men are the product of circumstances and of education, and that therefore modified men are the product of different circumstances and modified education, forgets that it is men, precisely, who do that circumstances change and that the educator himself needs to be educated. It leads, then, necessarily, to society in two parts, one of which is above society.
4. The coincidence of the modification of circumstances and of human activity can only be rationally conceived and understood as a revolutionary practice.

5. Feuerbach starts from religious self-alienation, from the unfolding of the world into a religious, imaginary, and real world. Its mission is to dissolve the religious world, reducing it to its earthly base. He does not notice that, after carrying out this task, the main thing remains to be done. Indeed, the fact that the earthly base separates from itself and is reflected in the clouds as an independent kingdom can only be explained by the tearing itself and the contradiction of this earthly basis with itself. Therefore, the first thing to do is to understand this in its contradiction and then revolutionize practically eliminating the contradiction. Therefore, after discovering, v. gr., in the earthly family the secret of the sacred family, one has to criticize theoretically and revolutionize practically that one.

6. Feuerbach, not content with abstract thought, appeals to sensory contemplation; but it does not conceive sensoriness as a practical human sensory activity.

7. Feuerbach dilutes the religious essence in the human essence. But the human essence is not something abstract inherent in each individual. It is, in its reality, the set of social relations.

8. Feuerbach, who does not deal with the critique of this real essence, is therefore obliged to make an abstraction of the historical trajectory, focusing for himself the religious feeling (Gemüt) and presupposing an abstract, isolated human individual.

9. In him, the human essence can only be conceived as “gender”, as an internal, mute generality, which merely unites the many individuals. Feuerbach does not see, therefore, that “religious feeling” is also a social product and that the abstract individual he analyzes belongs, in reality, to a certain form of society.

10. Social life is, in essence, practical. All the mysteries that lead the theory towards mysticism find their rational solution in human practice and in the understanding of that practice.

11. What most reaches the contemplative materialism, ie, the materialism that does not conceive the sensoriety as a practical activity, is to contemplate the different individuals within the “civil society.”

12. The point of view of the old materialism is civil society; that of new materialism, human society or socialized humanity.

13. Philosophers have only interpreted the world in different ways, but what is at issue is transforming it.