Reponse to Alex Lau (lau2.txt):
Alex has raised a number of important and incisive questions about the meaning of materialism, and how Marx's dialectic differs from Hegel's, etc. The following is my attempt to answer these questions.

Alex said:
(1) "Mediation - Marxist analysis used to pay attention on the macro level, forces of production, relations of production, and class structure, but often resorts to reductionism when it comes to the micro level"

It is true that the great Marxists of the 19th and early 20th century did not leave us any guide for an approach to psychology, personality, learning, language, etc. The interest in this discussion group in Vygotsky is partly motivated by the need people see to deal with this side of human existence. I am one of those who would rank Vygotsky among the great Marxists for this contribution. Unfortunately he died very young. 
Apart from Vygotsky's work, Marxism has no theory of personality, and Sartre, I agree, should be credited for having made an endeavour in this direction. Prior to Jung, Piaget and Vygotsky, I don't believe natural science had the basis for a theory of personality either. We have some catching up to do, unfortunately with poor resources.
However, I think the issue of the debasement of Marxism with what you call "reductionism" is something else. It is one thing to recognise that one lacks a scientific basis for dealing with certain aspects of human existence, it is another to substitute crudities for that lack. 

Alex said:
(2) "Material Dialectic - according to Sartre, history is dialectical because human praxis is dialectical and we can understand the dialectical character of social phenomena, the dialectic of experience, because we practice it".

Yes, but it begs the question, doesn't it? History is the totality of human practice, but why is human practice dialectical? My understanding of this is that human practice is dialectical because Nature is dialectical. 
Under Sartre's definition of "dialectics", ie. "the intelligibility of praxis", this is a tautology. But the same issue applies with other properties of thought: formal logic is valid because it describes relationships that objectively exist in Nature, and the same for all the various branches of mathematics, not only dialectics.
Thought (by definition) is how we are conscious of Nature, so it is by the study of thought (including logic, history of science, mathematics, etc) that we get to know the most general laws of Nature. 
I recommend the study of Hegel's Logic as a theory of cognition, but it is primarily a summing up of the most general laws of the movement of matter. Here, of course, I refer to Engels, and I do not share the view that Engels was at odds with Marx here. Only that Engels can be accused of "over-simplifiying", or of corrupting some thoughts "in the interests of popularisation", and of course, Lenin shares that view.
To refer to Marx himself, I think that his considered view (1873) is quite unambiguous:

"My dialectic method is not only different from the Hegelian, but is its direct opposite. To Hegel, the life-process of the human brain, i.e., the process of thinking, which, under the name of "the Idea", he even transforms into an independent subject, is the demiurgos of the real world, and the real world is only the external, phenomenal form of "the Idea". With me, on the contrary, the ideal is nothing else than the material world reflected by the human mind, and translated into forms of thought." [from The Afterword to the Second German Edition of CAPITAL]

Alex said:
(2a) "in what sense is Hegel's philosophy idealism? or in Marx's interpretation idealism?"

The question of idealism or materialism is the question of primacy of thought (or Spirit) to matter or vice versa. Objective idealism is compatible with almost consistent science. The great religions of the world are broadly-speaking in the camp of objective idealism. Most of the great religions have coped with natural science by some variant on the idea that God acts or expresses himself, through Nature, through natural laws, rather than actually intervening in Nature. Objective idealism is quite a different kettle of fish from subjective idealism. 
The problem lies in whether Nature approximates or partially expresses a law or a law approximates, or partially reflects Nature. Hegel's idealism is no great barrier in the Logic, but when Hegel moves to history for example, the idealism becomes a real problem, since there is an inevitable tendency to force each process studied into a pre-defined system, to confirm the presence of the action of God, or the Idea - the kind of trap of ourse, into which we are all liable to fall!

Alex said:
(2b) "what exactly does Marx mean when he inverted Hegel's dialectic? Does he mean the transformative method he found in Feuerbach?"

Alex, I am sure you have read all the texts on this question? to say the least! - can I respond to ths by commenting as per (2d) below?

Alex said:
(2c) "It seems unlikely Hegel means Absolute Idea in a religious sense like God and the world is his appearance."

I know what you mean! Religion seems so gross it's difficult to accept that some people really believe in it! But, according to Marx (Critique of Hegel's Philosophy in General, 1844) "having superseded religion and recognised it as a product of self-alienation, he [Hegel] still finds himself confirmed in religion as religion". And, as I remarked above, objective idealism is close in its meaning to religion, in so far as we are talking about the great religions of the world, which were the "official creeds" of the social systems in which natural science developed.

Alex said:
(2d) "... commodity, exchange value, etc., are as abstract categories as Being, Nothing and Becoming. If Marx means materialism in the sense of "real individuals, their activity and the material conditions of their life, both those which they find already existing and those produced by their activity " (German Ideology) then Sartre has his point in grounding his dialectic in human praxis".

The contrast between abstract and concrete is not at all the contrast between ideal and material, as I think is implied in your comment, a prejudice characteristic only of the crudest form of materialism, which could not really warrant the name of philosophical materialism at all.

You refer to Marx's "First Premises of Materialist Method" in The German Ideology: 

"The premises from which we begin are not arbitrary ones, not dogmas, but real premises from which abstraction can only be made in the imagination. They are real individuals, their activity and the material conditions under which they live, both those which they find already existing and those produced by their activity. These premises can thus be verified in a purely empirical way. The first premise of all human history is, of course, the existence of living human individuals. Thus the first fact to be established is the physical organisation of these individuals and their consequent relation to the rest of nature. Of course we cannot here go either into the actual physical nature of man, or into the natural conditions in which man finds himself - geological, orohydrographical, climatic and so on. The writing of history must always set out from these natural bases and their modification in the course of history through the action of men. Men can be distinguished from animals by consciousness, by religion or anything else you like. They themselves begin to distinguish themselves from animals as soon as they begin to *produce* their means of subsistence ..."

I think Sartre is correct to take as premise human praxis, if like Marx, he does so rather than setting out from ideal premises with the aim of creating a theory by formal deduction. But as Marx indicates, human beings distinguish themselves from nature by labour, and this act forms the starting point for history - but - in the beginning was Nature. In Marx's day there were historians who claimed to explain the nature of the various nations and peoples by reference to geographical features of their country, and Marx makes a point of the primacy of human labour, not geography, etc. Woman/man makes history, change Nature, but do not make Nature. Humanity is a part of, a product of Nature which distinguishes itself from Nature by labour. 

Alex said:
(3) "China - ... Sartre's phenomenology of group formation and of the role of groups in human history, his practico-inert, counter-finality, seriality etc., rendered the possibility of a new perspective in understanding China during Mao's era: ..."

Well, yes. I think Marxism was quite adequate to make a critique of all Mao's policies and historical and social analyses, but I think we have a lot of work to do to be able to negate this kind of practice. I know that in the mid-1920s there were very many of the Chinese Communist Party in the USSR and these almost entirely sided with the Left Opposition and almost none of them ever got back to China. Those few who did, found an Stalinised CCP when they got back and so far as I know never found the way to overcome this degeneration. Was it ever possible? Especially in a country which was 90% + peasantry, and with a CP basing itself on the peasant movement? Maybe not. But I agree, we certainly do need to develop this side of Marxism.