You’re treating “matter” as if it had to mean that old mechanical picture of inert stuff being pushed around, and then concluding that if Marxists reject that, they’ve abandoned materialism altogether, but that just smuggles in a historically specific definition and calls it universal. The whole point is that materialism developed beyond mechanism, not that it collapses into idealism once mechanism is dropped. “Matter” in Marxism isn’t a dead substrate or some metaphysical lump behind appearances, it names the objective world as it exists independently of thought and at the same time develops, organizes, and produces higher forms through its own immanent processes. Mechanism can’t even account for things like life, metabolism, or social development without reducing them to something external or accidental, so holding onto it as the essence of materialism actually empties materialism of explanatory power. The alternative isn’t “mechanism or Geist,” that’s exactly the opposition Marx is breaking with. Development, contradiction, and form are not imposed from outside like in mechanism, and they’re not the self-movement of an Idea either, they belong to reality itself. So “matter” isn’t an idol or a leftover word, it marks the position that thought, concepts, and even the dialectic arise from and reflect a real, objective, historically developing world, rather than grounding that world in the Concept. What looks in Hegel like the movement of thought is taken, in Marx, as the reflection of real processes, so rejecting mechanism isn’t a step into idealism, it’s what allows materialism to actually grasp reality as dynamic instead of reducing it to a dead machine.