1. The Concept of Human Nature
Of course, Marx was never tempted to assume that "human nature" was identical with that particular expression of human nature prevalent in his own society. In arguing against Bentham, Marx said: "To know what is useful for a dog, one must study dog nature. This nature itself is not to be deduced from the principle of utility. Applying this to man, he that would criticize all human acts, movements, relations, etc., by the principle of utility, must first deal with human nature in general, and then with human nature as modified in each historical epoch."  It must be noted that this concept of human nature is not, for Marx -- as it was not either for Hegel -an abstraction. It is the essence of man -- in contrast to the various forms of his historical existence -- and, as Marx said, "the essence of man is no abstraction inherent in each separate individual."  It must also be stated that this sentence from Capital, written by the "old Marx," shows the continuity of the concept of man's essence ( Wesen) which the young Marx wrote about in the Economic and Philosophical Manuscripts. He no longer used the term "essence" later on, as being abstract and unhistorical, but he clearly retained the notion of this essence in a more historical version, in the differentiation between "human nature in general" and "human nature as modified" with each historical period.
In line with this distinction between a general human nature and the specific expression of human nature in each culture, Marx distinguishes, as we have already mentioned above, two types of human drives and appetites: the constant or fixed ones, such as hunger and the sexual urge, which are an integral part of human nature, and which can be changed only in their form and the direction they take in various cultures, and the "relative" appetites, which are not an integral part of human nature but which "owe their origin to certain social structures and certain conditions of production and communication."  Marx gives as an example the needs produced by the capitalistic structure of society. "The need for money," he wrote in the Economic and Philosophical Manuscripts, "is therefore the real need created by the modern economy, and the only need which it creates.... This is shown subjectively, partly in the fact that the expansion of production and of needs becomes an ingenious and always calculating subservience to inhuman, depraved, unnatural, and imaginary appetites." 
Man's potential, for Marx, is a given potential; man is, as it were, the human raw material which, as such, cannot be changed, just as the brain structure has remained the same since the dawn of history. Yet, man does change in the course of history; he develops himself; he transforms himself, he is the product of history; since he makes his history, he is his own product. History is the history of man's self-realization; it is nothing but the self-creation of man through the process of his work and his production: "the whole of what is called world history is nothing but the creation of man by human labor, and the emergence of nature for man; he therefore has the evident and irrefutable proof of his self-creation, of his own origins." 
2. Man's self-activity
Marx's concept of man is rooted in Hegel's thinking. Hegel begins with the insight that appearance and essence do not coincide. The task of the dialectical thinker is "to distinguish the essential from the apparent process of reality, and to grasp their relations."  Or, to put it differently, it is the problem of the relationship between essence and existence. In the process of existence, the essence is realized, and at the same time, existing means a return to the essence. "The world is an estranged and untrue world so long as man does not destroy its dead objectivity and recognize himself and his own life 'behind' the fixed form of things and laws. When he finally wins this self-consciousness, he is on his way not only to the truth of himself, but also of his world. And with the recognition goes the doing. He will try to put this truth into action, and make the world what it essentially is, namely, the fulfillment of man's self-consciousness."  For Hegel, knowledge is not obtained in the position of the subjectobject split, in which the object is grasped as something separated from and opposed to the thinker. In order to know the world, man has to make the world his own. Man and things are in a constant transition from one suchness into another; hence "a thing is for itself only when it has posited (gesetzt) all its determinates and made them moments of its self-realization, and is thus, in all changing conditions, always 'returning to itself'."  In this process "entering into itself becomes essence." This essence, the unity of being, the identity throughout change is, according to Hegel, a process in which "everything copes with its inherent contradictions and unfolds itself as a result." "The essence is thus as much historical as ontological. The essential potentialities of things realize themselves in the same comprehensive process that establishes their existence. The essence can 'achieve' its existence when the potentialities of things have ripened in and through the conditions of reality. Hegel describes this process as the transition to actuality."  In contrast to positivism, for Hegel "facts are facts only if related to that which is not yet fact and yet manifests itself in the given facts as a real possibility. Or, facts are what they are only as moments in a process that leads beyond them to that which is not yet fulfilled in fact."
The culmination of all of Hegel's thinking is the concept of the potentialities inherent in a thing, of the dialectical process in which they manifest themselves, and the idea that this process is one of active movement of these potentialities. This emphasis on the active process within man is already to be found in the ethical system of Spinoza. For Spinoza, all affects were to be divided into passive affects (passions), through which man suffers and does not have an adequate idea of reality, and into active affects (actions) (generosity and fortitude) in which man is free and productive. Goethe, who like Hegel was influenced by Spinoza in many ways, developed the idea of man's productivity into a central point of his philosophical thinking. For him all decaying cultures are characterized by the tendency for pure subjectivity, while all progressive periods try to grasp the world as it is, by one's own subjectivity, but not separate from it.  He gives the example of the poet: "as long as he expresses only these few subjective sentences, he can not yet be called a poet, but as soon as he knows how to appropriate the world for himself, and to express it, he is a poet. Then he is inexhaustible, and can be ever new, while his purely subjective nature has exhausted itself soon and ceases to have anything to say."  "Man", says Goethe, "knows himself only inasmuch as he knows the world; he knows the world only within himself and he is aware of himself only within the world. Each new object truly recognized, opens up a new organ within ourselves."  Goethe gave the most poetic and powerful expression to the idea of human productivity in his Faust. Neither possession, nor power, nor sensuous satisfaction, Faust teaches, can fulfill man's desire for meaning in his life; he remains in all this separate from the whole, hence unhappy. Only in being productively active can man make sense of his life, and while he thus enjoys life, he is not greedily holding on to it. He has given up the greed for having, and is fulfilled by being; he is filled because he is empty; he is much, because he has little.  Hegel gave the most systematic and profound expression to the idea of the productive man, of the individual who is he, inasmuch as he is not passive-receptive, but actively related to the world; who is an individual only in this process of grasping the world productively, and thus making it his own. He expressed the idea quite poetically by saying that the subject wanting to bring a content to realization does so by "translating itself from the night of possibility into the day of actuality." For Hegel the development of all individual powers, capacities and potentialities is possible only by continuous action, never by sheer contemplation or receptivity. For Spinoza, Goethe, Hegel, as well as for Marx, man is alive only inasmuch as he is productive, inasmuch as he grasps the world outside of himself in the act of expressing his own specific human powers, and of grasping the world with these powers.
Inasmuch as man is not productive, inasmuch as he is receptive and passive, he is nothing, he is dead. In this productive process, man realizes his own essence, he returns to his own essence, which in theological language is nothing other than his return to God.
For Marx man is characterized by the "principle of movement," and it is significant that he quotes the great mystic Jacob Boehme in connection with this point.  The principle of movement must not be understood mechanically but as a drive, creative vitality, energy; human passion for Marx "is the essential power of man striving energetically for its object."
The concept of productivity as against that of receptivity can be understood more easily when we read how Marx applied it to the phenomenon of love. "Let us assume man to be man," he wrote, "and his relation to the world to be a human one. Then love can only be exchanged for love, trust for trust, etc. If you wish to influence other people you must be a person who really has a stimulating and encouraging effect upon others. Every one of your relations to man and to nature must be a specific expression corresponding to the object of your will, of your real individual life. If you love without evoking love in return, i.e., if you are not able, by the manifestation of yourself as a loving person, to make yourself a beloved person, then your love is impotent and a misfortune."  Marx expressed also very specifically the central significance of love between man and woman as the immediate relationship of human being to human being. Arguing against a crude communism which proposed the communalization of all sexual relation, Marx wrote: "In the relationship with woman, as the prey and the handmaid of communal lust, is expressed the infinite degradation in which man exists for himself; for the secret of this relationship finds its unequivocal, incontestable, open and revealed expression in the relation of man to woman and in the way in which the direct and natural species relationship is conceived. The immediate, natural and necessary relation of human being to human being is also the relation of man to woman. In this natural species relationship man's relation to nature is directly his relation to man, and his relation to man is directly his relation to nature, to his own natural function. Thus, in this relation is sensuously revealed, reduced to an observable fact, the extent to which human nature has become nature for man and to which nature has become human nature for him. From this relationship man's whole level of development can be assessed. It follows from the character of this relationship how far man has become, and has understood himself as, a species-being, a human being. The relation of man to woman is the most natural relation of human being to human being. It indicates, therefore, how far man's natural behavior has become human, and how far his human essence has become a natural essence for him, how far his human nature has become nature for him. It also shows how far man's needs have become human needs, and consequently how far the other person, as a person, has become one of his needs, and to what extent he is in his individual existence at the same time a social being." 
It is of the utmost importance for the understanding of Marx's concept of activity to understand his idea about the relationship between subject and object. Man's senses, as far as they are crude animal senses, have only a restricted meaning. "For a starving man the human form of food does not exist, but only its abstract character as food. It could just as well exist in the most crude form, and it is impossible to say in what way this feeding activity would differ from that of animals. The needy man, burdened with cares, has no appreciation of the most beautiful spectacle."  The senses which man has, so to speak, naturally, need to be formed by the objects outside of them. Any object can only be confirmation of one of my own faculties. "For it is not only the five senses but also the so-called spiritual senses, the practical senses (desiring, loving, etc.) in brief, human sensibility and the human character of the senses which can only come into being through the existence of its object, through humanized nature." The objects, for Marx, "confirm and realize his [man's] individuality... The manner in which these objects become his own depends upon the nature of the object and the nature of the corresponding faculty;...The distinctive character of each faculty is precisely its characteristic essence and thus also the characteristic mode of its objectification, of its objectively real, living being. It is therefore not only in thought, but through all the senses that man is affirmed in the objective world." 
By relating himself to the objective world, through his powers, the world outside becomes real to man, and in fact it is only "love" which makes man truly believe in the reality of the objective world outside himself.  Subject and object cannot be separated. "The eye has become a human eye when its object has become a human, social object, created by man and destined for him...They [the senses] relate themselves to the thing for the sake of the thing, but the thing itself is an objective human relation to itself and to man, and vice versa. Need and enjoyment have thus lost their egoistic character, and nature has lost its mere utility by the fact that its utilization has become human utilization. (In effect, I can only relate myself in a human way to a thing when the thing is related in a human way to man.)" 
For Marx, "Communism is the positive abolition of private property,  of human self-alienation, and thus the real appropriation of human nature through and for man. It is, therefore, the return of man himself as a social, i.e., really human being, a complete and conscious return which assimilates all the wealth of previous development. Communism as a fully developed naturalism is humanism and as a fully developed humanism is naturalism. It is the definitive resolution of the antagonism between man and nature, and between man and man. It is the true solution of the conflict between existence and essence, between objectification and self-affirmation, between freedom and necessity, between individual and species. It is the solution of the riddle of history and knows itself to be this solution."  This active relationship to the objective world, Marx calls "productive life." "It is life creating life. In the type of life activity resides the whole character of a species, its species-character; and free, conscious activity is the species-character of human beings."  What Marx means by "species-character" is the essence of man; it is that which is universally human, and which is realized in the process of history by man through his productive activity.
From this concept of human self-realization, Marx arrives at a new concept of wealth and poverty, which is different from wealth and poverty in political economy. "It will be seen from this," says Marx, "how, in place of the wealth and poverty of political economy, we have the wealthy man and the plenitude of human need. The wealthy man is at the same time one who needs a complex of human manifestations of life, and whose own self-realization exists as an inner necessity, a need. Not only the wealth but also the poverty of man acquires, in a socialist perspective, a human and thus a social meaning. Poverty is the passive bond which leads man to experience a need for the greatest wealth, the other person. The sway of the objective entity within me; the sensuous outbreak of my life-activity, is the passion which here becomes the activity of my being."  The same idea was expressed by Marx some years earlier: "The existence of what I truly love [specifically he refers here to freedom of the press] is felt by me as a necessity, as a need, without which my essence cannot be fulfilled, satisfied, complete." 
"Just as society at its beginnings finds, through the development of private property with its wealth and poverty (both intellectual and material), the materials necessary for this cultural development, so the fully constituted society produces man in all the plenitude of his being, the wealthy man endowed with all the senses, as an enduring reality. It is only in a social context that subjectivism and objectivism, spiritualism and materialism, activity and passivity, cease to be antinomies and thus cease to exist as such antinomies. The resolution of the theoretical contradictions is possible only through practical means, only through the practical energy of man. Their resolution is not by any means, therefore, only a problem of knowledge, but is a real problem of life which philosophy was unable to solve precisely because it saw there a purely theoretical problem." 
Corresponding to his concept of the wealthy man is Marx's view of the difference between the sense of having and the sense of being. "Private property," he says, "has made us so stupid and partial that an object is only ours when we have it, when it exists for us as capital or when it is directly eaten, drunk, worn, inhabited, etc., in short, utilized in some way. Although private property itself only conceives these various forms of possession as means of life, and the life for which they serve as means is the life of private property -- labor and creation of capital. Thus all the physical and intellectual senses have been replaced by the simple alienation of all these senses; the sense of having. The human being had to be reduced to this absolute poverty in order to be able to give birth to all his inner wealth." 
Marx recognized that the science of capitalistic economy, despite its worldly and pleasure-seeking appearance, "is a truly moral science, the most moral of all sciences. Its principal thesis is the renunciation of life and of human needs. The less you eat, drink, buy books, go to the theatre or to balls, or to the public house [ Br., pub], and the less you think, love, theorize, sing, paint, fence, etc., the more you will be able to save and the greater will become your treasure which neither moth nor rust will corrupt -- your capital. The less you are, the less you express your life, the more you have, the greater is your alienated life and the greater is the saving of your alienated being. Everything which the economist takes from you in the way of life and humanity, he restores to you in the form of money and wealth. And everything which you are unable to do, your money can do for you; it can eat, drink, go to the ball and to the theatre. It can acquire art, learning, historical treasures, political power; and it can travel. It can appropriate all these things for you, can purchase everything; it is the true opulence. But although it can do all this, it only desires to create itself, and to buy itself, for everything else is subservient to it. When one owns the master, one also owns the servant, and one has no need of the master's servant. Thus all passions and activities must be submerged in avarice. The worker must have just what is necessary for him to want to live, and he must want to live only in order to have this." 
The aim of society, for Marx, is not the production of useful things as an aim in itself. One easily forgets, he says, "that the production of too many useful things results in too many useless people."  The contradictions between prodigality and thrift, luxury and abstinence, wealth and poverty, are only apparent because the truth is that all these antinomies are equivalent. It is particularly important to understand this position of Marx today, when both the Communist, and most of the Socialist parties, with some notable exceptions like the Indian, also Burmese and a number of European and American socialists, have accepted the principle which underlies all capitalist systems, namely, that maximum production and consumption are the unquestionable goals of society. One must of course not confuse the aim of overcoming the abysmal poverty which interferes with a dignified life, with the aim of an ever-increasing consumption, which has become the supreme value for both Capitalism and Krushchevism. Marx's position was quite clearly on the side of the conquest of poverty, and equally against consumption as a supreme end.
Independence and freedom, for Marx, are based on the act of self-creation. "A being does not regard himself as independent unless he is his own master, and he is only his own master when he owes his existence to him self. A man who lives by the favor of another considers himself a dependent being. But I live completely by another person's favor when I owe to him not only the continuance of my life but also its creation; when he is its source. My life has necessarily such a cause outside itself if it is not my own creation."  Or, as Marx put it, man is independent only "...if he affirms his individuality as a total man in each of his relations to the world, seeing, hearing, smelling, tasting, feeling, thinking, willing, loving -- in short, if he affirms and expresses all organs of his individuality," if he is not only free from but also free to.
For Marx the aim of socialism was the emancipation of man, and the emancipation of man was the same as his self-realization in the process of productive relatedness and oneness with man and nature. The aim of socialism was the development of the individual personality. What Marx would have thought of a system such as Soviet communism he expressed very clearly in a statement of what he called "crude communism," and which referred to certain communist ideas and practices of his time. This crude communism "appears in a double form; the domination of material property looms so large that it aims to destroy everything which is incapable of being possessed by everyone as private property. It wishes to eliminate talent, etc., by force. Immediate physical possession seems to it the unique goal of life and existence. The role of worker is not abolished but is extended to all men. The relation of private property remains the relation of the community to the world of things. Finally, this tendency to oppose general private property to private property is expressed in an animal form; marriage (which is incontestably a form of exclusive private property) is contrasted with the community of women,  in which women become communal and common property. One may say that this idea of the community of women is the open secret of this entirely crude and unreflective communism. Just as women are to pass from marriage to universal prostitution, so the whole world of wealth (i.e., the objective being of man) is to pass to the relation of universal prostitution with the community. This communism, which negates the personality of man in every sphere, is only the logical expression of private property, which is this negation. Universal envy setting itself up as a power is only a camouflaged form of cupidity which reestablishes itself and satisfies itself in a different way. The thoughts of every individual private property are at least directed against any wealthier private property, in the form of envy and the desire to reduce everything to a common level; so that this envy and levelling in fact constitute the essence of competition. Crude communism is only the culmination of such envy and levelling-down on the basis of a preconceived minimum. How little this abolition of private property represents a genuine appropriation is shown by the abstract negation of the whole world of culture and civilization, and the regression to the unnatural simplicity of the poor and wantless individual who has not only not surpassed private property but has not yet even attained to it. The community is only a community of work and of equality of wages paid out by the communal capital, by the community as universal capitalist. The two sides of the relation are raised to a supposed universality; labor as a condition in which everyone is placed, and capital as the acknowledged universality and power of the community." 
Marx's whole concept of the self-realization of man can be fully understood only in connection with his concept of work. First of all, it must be noted that labor and capital were not at all for Marx only economic categories; they were anthropological categories, imbued with a value judgment which is rooted in his humanistic position. Capital, which is that which is accumulated, represents the past; labor, on the other hand is, or ought to be when it is free, the expression of life. "In bourgeois society," says Marx in the Communist Manifesto,"...the past dominates the present. In communist society the present dominates the past. In bourgeois society, capital is independent and has individuality, while the living person is dependent and has no individuality." Here again, Marx follows the thought of Hegel, who understood labor as the "act of man's self-creation." Labor, to Marx, is an activity, not a commodity. Marx originally called man's function "self-activity," not labor, and spoke of the "abolition of labor" as the aim of socialism. Later, when he differentiated between free and alienated labor, he used the term "emancipation of labor."
"Labor is, in the first place, a process in which both man and nature participate, and in which man of his own accord starts, regulates, and controls the material reactions between himself and nature. He opposes himself to nature as one of her own forces, setting in motion arms and legs, head and hands, the natural forces of his body, in order to appropriate nature's productions in a form adapted to his own wants. By thus acting on the external world and changing it, he at the same time changes his own nature. He develops his slumbering powers and compels them to act in obedience to his sway. We are not now dealing with those primitive instinctive forms of labor that remind us of the mere animal. An immeasurable interval of time separates the state of things in which a man brings his labor power to market for sale as a commodity, from that state in which human labor was still in its first instinctive stage. We presuppose labor in a form that stamps it as exclusively human. A spider conducts operations that resemble those of a weaver, and a bee puts to shame many an architect in the construction of her cells. But what distinguishes the worst architect from the best of bees is this, that the architect raises his structure in imagination before he erects it in reality. At the end of every labor process, we get a result that already existed in the imagination of the laborer at its commencement. He not only effects a change of form in the material on which he works, but he also realizes a purpose of his own that gives the law to his modus operandi, and to which he must subordinate his will. And this subordination is no mere momentary act. Besides the exertion of the bodily organs, the process demands that, during the whole operation, the workman's will be steadily in consonance with his purpose. This means close attention. The less he is attracted by the nature of the work, and the mode in which it is carried on, and the less, therefore, he enjoys it as something which gives play to his bodily and mental powers, the more close his attention is forced to be." 
Labor is the self-expression of man, an expression of his individual physical and mental powers. In this process of genuine activity man develops himself, becomes himself; work is not only a means to an end -- the product -- but an end in itself, the meaningful expression of human energy; hence work is enjoyable.
Marx's central criticism of capitalism is not the injustice in the distribution of wealth; it is the perversion of labor into forced, alienated, meaningless labor, hence the transformation of man into a "crippled monstrosity." Marx's concept of labor as an expression of man's individuality is succinctly expressed in his vision of the complete abolition of the lifelong submersion of a man in one occupation. Since the aim of human development is that of the development of the total, universal man, man must be emancipated from the crippling influence of specialization. In all previous societies, Marx writes, man has been "a hunter, a fisherman, a shepherd, or a critical critic, and must remain so if he does not want to lose his means of livelihood; while in communist society, where nobody has one exclusive sphere of activity but each can become accomplished in any branch he wishes, society regulates the general production and thus makes it possible for me to do one thing today and another tomorrow, to hunt in the morning, fish in the afternoon, rear cattle in the evening, criticize after dinner, just as I have a mind, without ever becoming hunter, fisherman, shepherd or critic." 
There is no greater misunderstanding or misrepresentation of Marx than that which is to be found, implicitly or explicitly, in the thought of the Soviet Communists, the reformist socialists, and the capitalist opponents of socialism alike, all of whom assume that Marx wanted only the economic improvement of the working class, and that he wanted to abolish private property so that the worker would own what the capitalist now has. The truth is that for Marx the situation of a worker in a Russian "socialist" factory, a British state-owned factory, or an American factory such as General Motors, would appear essentially the same. This, Marx expresses very clearly in the following:
"An enforced increase in wages (disregarding the other difficulties, and especially that such an anomaly could only be maintained by force) would be nothing more than a better remuneration of slaves, and would not restore, either to the worker or to the work, their human significance and worth.
"Even the equality of incomes which Proudhon demands would only change the relation of the presentday worker to his work into a relation of all men to work. Society would then be conceived as an abstract capitalist." 
The central theme of Marx is the transformation of alienated, meaningless labor into productive, free labor, not the better payment of alienated labor by a private or "abstract" state capitalism.