1) Premise 1 (The Claim): Objective reality is fundamentally unknowable. All we have access to are our own perceptions, ideas, and sense data.
2) Implication: We are trapped behind a "veil of perception." We cannot compare our ideas to the "world-in-itself" to check their accuracy. The external world becomes a hypothetical cause for our internal experiences.
3) Logical Extension: If we cannot know the external world, we also cannot know that other minds exist. Other people are part of the external world; we only perceive their bodies and behaviors, not their consciousness.
4) Conclusion (Solipsism): The only thing one can truly know to exist is one's own mind. The external world, other people, the past, and the future could all be illusions or constructs of one's own consciousness.
From this perspective, any philosophy that denies direct or reliable access to objective reality is on a slippery slope to this intellectually barren and practically unlivable position.
The response isn't to claim we have infallible access to reality, but that the "unknowability" thesis is itself flawed because it relies on an impossible standard of knowledge. The core Marxist rebuttal, drawn from Marx's Theses on Feuerbach, is that we don't just think about reality; we interact with it and change it. Human practice is the proof of objectivity.
>The chief defect of all hitherto existing materialism – that of Feuerbach included – is that the thing, reality, sensuousness, is conceived only in the form of the object or of contemplation, but not as sensuous human activity, practice, not subjectively. Hence, in contradistinction to materialism, the active side was developed abstractly by idealism – which, of course, does not know real, sensuous activity as such[…]
>The question whether objective truth can be attributed to human thinking is not a question of theory but is a practical question. Man must prove the truth — i.e. the reality and power, the this-sidedness of his thinking in practice. The dispute over the reality or non-reality of thinking that is isolated from practice is a purely scholastic question[…]
>The philosophers have only interpreted the world, in various ways; the point is to change it. https://www.marxists.org/archive/marx/works/1845/theses/theses.htmIf I have a theory of aerodynamics and build an airplane that flies, my theory has been validated not by its correspondence to an inaccessible "thing-in-itself," but by its successful application in the real, material world. The plane's flight is a practical, material test.
Dialectical Materialism rejects the rigid subject-object dichotomy that creates the problem. Consciousness is not a sealed room looking out at a world it cannot touch. It is a product of the material world (the brain) that actively engages with that world. Knowledge is not a mirror of nature but a process of increasingly accurate reflection through practice.
>In the social production of their existence, men inevitably enter into definite relations, which are independent of their will, namely relations of production appropriate to a given stage in the development of their material forces of production[…] The mode of production of material life conditions the general process of social, political and intellectual life. It is not the consciousness of men that determines their existence, but their social existence that determines their consciousness.https://www.marxists.org/archive/marx/works/1859/critique-pol-economy/preface.htmMarxism does not arrive at "Complete Knowledge" in the traditional, philosophical sense of a final and perfect system of truth that ends all inquiry. In fact, the demand for "Complete Knowledge" is precisely the kind of metaphysical, ahistorical thinking that dialectics sets out to overcome. Knowledge is about a material world that is in constant flux. Since the object of knowledge (reality) is itself processual and unfinished, our knowledge of it must also be processual and unfinished. History and nature develop through contradictions and negations. There is no final, harmonious end-state of knowledge because the material world itself has no such final state. New contradictions and new phenomena constantly arise.
>The sovereignty of thought is realised in a number of extremely unsovereignly-thinking human beings; the knowledge which has an unconditional claim to truth is realised in a number of relative errors; neither the one nor the other [i.e., neither absolutely true knowledge, nor sovereign thought] can be fully realised except through an endless eternity of human existence. https://www.marxists.org/archive/lenin/works/1908/mec/two5.htmA theory is "objectively true" not because it perfectly mirrors the noumenal world, but because it allows us to accurately predict outcomes and successfully manipulate the material world. A social theory is "true" if it correctly identifies the contradictions within a society and provides a guide for action that successfully leads to its revolutionary transformation. The success of the practice validates the theory.
>The standpoint of life, of practice, should be first and fundamental in the theory of knowledge. https://www.marxists.org/archive/lenin/works/1908/mec/two6.htmMarxism claims a kind of "absolute" knowledge, but it is structural and historical, not factual and complete. The core argument is that the proletariat, by virtue of its objective position within the capitalist mode of production, is the one social class capable of achieving a "total" or "absolute" understanding of society as a whole. The bourgeoisie has an interest in understanding the parts (markets, profits) but must mystify the whole (exploitation, crisis), because understanding the whole would mean understanding its own historical transience. The proletariat, as the "universal class" whose emancipation requires the emancipation of all, has an interest in understanding the total system of its own exploitation. Its perspective is not partial but totalizing.
This is the "absolute" knowledge of the laws of motion of capitalism and its place in human history. It is the knowledge of the fundamental social totality, which Marx aimed to provide in Capital.
>The Marxist doctrine is omnipotent because it is true. It is comprehensive and harmonious, and provides men with an integral world outlook irreconcilable with any form of superstition, reaction, or defence of bourgeois oppression.https://www.marxists.org/archive/lenin/works/1913/mar/x01.htm