Can you quote a materialist in context that used that expression? Maybe that would help with the confusion.I don't know what "unquestionable essence" is, and neither does anyone else, but that doesn't stop vocal materialists from claiming it for their worldview.
Marcuse is a Marxist, hence a materialist. Eros and Civilization posits a change in human consciousness through the evolution of technology, increasing material abundance, and societal transformation.I'm not sure how Marcuse is supposed to clarify anything about materialist possibilities.
As I have repeatedly noted, not all materialists think "consciousness is only epiphenomenal". Nor would it be inconsistent for a materialist to believe consciousness could be causal in an argument such as this:
1- Consciousness exists.
2- Everything that exists is material.
3- Therefore, consciousness is material.
4- Since consciousness is material, it can have causal effect on other material things.