> In fact we are not at present able to explain at all fully the mental
> states of individuals. I would suspect that except in very rare cases
> (e.g., brain damage of a particular sort, such as the brain damage that
> made a painter unable to either see or imagine color) those mental
> states cannot be separated _either_ from the social relations
> (activity)
> in which the individuals find themselves enmeshed or from the activity
> of the brain.
I don't think Marx makes social relations "explain" "mental states" in the way this seems to suppose.
What social relations explain is the degree of development of "mind". A fully developed mind defines the "universally developed individual". As I've pointed out before, one essential characteristic of such an individual is found in the "mental state" associated with "willing". The will of a universally developed individual is both a "will proper" and a "universal will". A "will proper" is a will fully open to self-determination e.g. it is not in any way determined, as are "animal" wills, by "instinct". A "universal will" is one whose content is the product of rational self-determination. According to Marx, the ethical content of such a will would be relations of "mutual recognition". Such relations can only be realized through the rationally self-determined willing and acting of individuals. (This isn't just Marx's point; it's also e.g. Goethe's at the end of Faust.)
Social relations of production, according to Marx, constitute the "school" in which the process of "education" [bildung] which develops mind to "reason" takes place, the model for this being the role Hegel assigns to the master/slave relation in just such a process in the Phenomenology. The proletariat develops the capacity to act as the "architect" of relations of mutual recognition by going through "the stern but steeling school of labour" where "the severe discipline of capital, acting on succeeding generations [Geschlechter], has developed general industriousness as the general property of the new species [Geschlecht]".
"When socialist writers ascribe this world-historic role to the proletariat, it is not at all, as Critical Criticism pretends to believe, because they regard the proletarians as gods. Rather the contrary. Since in the fully-formed proletariat the abstraction of all humanity, even of the semblance of humanity, is practically complete; since the conditions of life of the proletariat sum up all the conditions of life of society today in their most inhuman form; since man has lost himself in the proletariat, yet at the same time has not only gained theoretical consciousness of that loss, but through urgent, no longer removable, no longer disguisable, absolutely imperative need -- the practical expression of necessity -- is driven directly to revolt against this inhumanity, it follows that the proletariat can and must emancipate itself. But it cannot emancipate itself without abolishing the conditions of its own life. It cannot abolish the conditions of its own life without abolishing all the inhuman conditions of life of society today which are summed up in its own situation. Not in vain does it go through the stern but steeling school of labour. It is not a question of what this or that proletarian, or even the whole proletariat, at the moment regards as its aim. It is a question of what the proletariat is, and what, in accordance with this being, it will historically be compelled to do. Its aim and historical action is visibly and irrevocably foreshadowed in its own life situation as well as in the whole organization of bourgeois society today." Holy Family
“The great historic quality of capital is to create this surplus labour, superfluous labour from the standpoint of mere use value, mere subsistence; and its historic destiny [Bestimmung] is fulfilled as soon as, on one side, there has been such a development of needs that surplus labour above and beyond necessity has itself become a general need arising out of individual needs themselves—and, on the other side, when the severe discipline of capital, acting on succeeding generations [Geschlechter], has developed general industriousness as the general property of the new species [Geschlecht]—and, finally, when the development of the productive powers of labour, which capital incessantly whips onward with its unlimited mania for wealth, and of the sole conditions in which this mania can be realized, have flourished to the stage where the possession and preservation of general wealth require a lesser labour time of society as a whole, and where the labouring society relates scientifically to the process of its progressive reproduction, its reproduction in a constantly greater abundance; hence where labour in which a human being does what a thing could do has ceased. Accordingly, capital and labour relate to each other here like money and commodity; the former is the general form of wealth, the other only the substance destined for immediate consumption. Capital's ceaseless striving towards the general form of wealth drives labour beyond the limits of its natural paltriness [Naturbedürftigkeit], and thus creates the material elements for the development of the rich individuality which is as all-sided in its production as in its consumption, and whose labour also therefore appears no longer as labour, but as the full development of activity itself, in which natural necessity in its direct form has disappeared; because a historically created need has taken the place of the natural one. This is why capital is productive; i.e. an essential relation for the development of the social productive forces. It ceases to exist as such only where the development of these productive forces themselves encounters its barrier in capital itself.” (Marx, Grundrisse, p. 325)
When this "rich individuality" has been realized, individuals will cease to reify their social relations i.e. fail to see them as "their product" and mistakenly attribute to them an "alien and independent character". The social relations of such individuals will be "their own communal [gemeinschaftlich] relations, are hence also subordinated to their own communal control".
“It has been said and may be said that this [‘the way in which their own exchange and their own production confront individuals as an objective relation which is independent of them’] is precisely the beauty and the greatness of it [‘the world market’]: this spontaneous interconnection, this material and mental metabolism which is independent of the knowing and willing of individuals, and which presupposes their reciprocal independence and indifference. And, certainly, this objective connection is preferable to the lack of any connection, or to a merely local connection resting on blood ties, or on primeval, natural or master-servant relations. Equally certain is it that individuals cannot gain mastery over their own social interconnections before they have created them. But it is an insipid notion to conceive of this merely objective bond as a spontaneous, natural attribute inherent in individuals and inseparable from their nature (in antithesis to their conscious knowing and willing). This bond is their product. It is a historic product. It belongs to a specific phase of their development. The alien and independent character in which It presently exists vis-à-vis individuals proves only that the latter are still engaged in the creation of the conditions of their social life, and that have not yet begun, on the basis of these conditions, to live it. It is the bond natural to individuals within specific and limited relations of production. Universally developed individuals, whose social relations, as their own communal [gemeinschaftlich] relations, are hence also subordinated to their own communal control, are no product of nature, but of history. The degree and the universality of the development of wealth where this individuality becomes possible supposes production on the basis of exchange values as a prior condition, whose universality produces not only the alienation of the individual from himself and from others, but also the universality and the comprehensiveness of his relations and capacities.” (Marx, Grundrisse, pp. 161-2)
You are attributing an ontology to Marx that has no logical space for the idea of persons as potentially "universally developed individuals" and, hence, for the ideas of a "will proper" and a "universal will". Consequently, it can't accomodate the "cause" that Marx, following Kant and Aristotle, treats as defining human labour.
"By right we ought only to describe as art, production through freedom, i.e. through a will that places reason at the basis of its actions. For although we like to call the product of bees (regularly built cells of wax) a work of art, this is only by way of analogy; as soon as we feel that this work of theirs is based on no proper rational deliberation, we say that it is a product of nature (of instinct).
"If, as sometimes happens, in searching through a bog we come upon a bit of shaped wood, we do not say, this is a product of nature, but of art. Its producing cause has conceived a purpose to which the plank owes its form. Elsewhere too we should see art in everything which is made, so that a representative of it in its cause must have preceded its actual existence (as even in the case of bees), though without the effect of it even being capable of being thought. But if we call anything absolutely a work of art, in order to distinguish it from a natural effect, we always understand by that a work of man." (Kant, Critique of Judgment, pp.145-6)
"We presuppose labour in a form in which it is an exclusively human characteristic. A spider conducts operations which resemble those of the weaver, and a bee would put many a human architect to shame by the construction of its honeycomb cells. But what distinguishes the worst architect from the best of bees is that the architect builds the cell in his mind before he constructs it in wax. At the end of every labour process, a result emerges which had already been conceived by the worker at the beginning, hence already existed ideally. Man not only effects a change of form in the materials of nature; he also realizes his own purpose in those materials. And this is a purpose he is conscious of, it determines the mode of his activity with the rigidity of a law, and he must subordinate his will to it." (Marx, Capital, vol. 1, pp. 283-4)
Ted