Before Marx, materialism examined the problem of knowledge apart from the social nature of man and apart from his historical development, and was therefore incapable of understanding the dependence of knowledge on social practice, that is, the dependence of knowledge on production and the class struggle.

Above all, Marxists regard man's activity in production as the most fundamental practical activity, the determinant of all his other activities. Man's knowledge depends mainly on his activity in material production, through which he comes gradually to understand the phenomena, the properties and the laws of nature, and the relations between himself and nature; and through his activity in production he also gradually comes to understand, in varying degrees, certain relations that exist between man and man. None of this knowledge can be acquired apart from activity in production. In a classless society every person, as a member of society, joins in common effort with the other members, enters into definite relations of production with them and engages in production to meet man's material needs. In all class societies, the members of the different social classes also enter, in different ways, into definite relations of production and engage in production to meet their material needs. This is the primary source from which human knowledge develops.

Man's social practice is not confined to activity in production, but takes many other forms—class struggle, political life, scientific and artistic pursuits; in short, as a social being, man participates in all spheres of the practical life of society. Thus man, in varying degrees, comes to know the different relations between man and man, not only through his material life but also through his political and cultural life (both of which are intimately bound up with material life). Of these other types of social practice, class struggle in particular, in all its various forms, exerts a profound influence on the development of man's knowledge. In class society everyone lives as a member of a particular class, and every kind of thinking, without exception, is stamped with the brand of a class.

Marxists hold that in human society activity in production develops step by step from a lower to a higher level and that consequently man's knowledge, whether of nature or of society, also develops step by step from a lower to a higher level, that is, from the shallower to the deeper, from the one-sided to the many-sided. For a very long period in history, men were necessarily confined to a one-sided understanding of the history of society because, for one thing, the bias of the exploiting classes always distorted history and, for another, the small scale of production limited man's outlook. It was not until the modern proletariat emerged along with immense forces of production (large-scale industry) that man was able to acquire a comprehensive, historical understanding of the development of society and turn this knowledge into a science, the science of Marxism.

Marxists hold that man's social practice alone is the criterion of the truth of his knowledge of the external world. What actually happens is that man's knowledge is verified only when he achieves the anticipated results in the process of social practice (material production, class struggle or scientific experiment). If a man wants to succeed in his work, that is, to achieve the anticipated results, he must bring his ideas into correspondence with the laws of the objective external world; if they do not correspond, he will fail in his practice. After he fails, he draws his lessons, corrects his ideas to make them correspond to the laws of the external world, and can thus turn failure into success; this is what is meant by "failure is the mother of success" and "a fall into the pit, a gain in your wit". The dialectical-materialist theory of knowledge places practice in the primary position, holding that human knowledge can in no way be separated from practice and repudiating all the erroneous theories which deny the importance of practice or separate knowledge from practice. Thus Lenin said, "Practice is higher than (theoretical) knowledge, for it has not only the dignity of universality, but also of immediate actuality." The Marxist philosophy of dialectical materialism has two outstanding characteristics. One is its class nature: it openly avows that dialectical materialism is in the service of the proletariat. The other is its practicality: it emphasizes the dependence of theory on practice, emphasizes that theory is based on practice and in turn serves practice. The truth of any knowledge or theory is determined not by subjective feelings, but by objective results in social practice. Only social practice can be the criterion of truth. The standpoint of practice is the primary and basic standpoint in the dialectical materialist theory of knowledge. Here Mao references Karl Marx's "Theses on Feuerbach," Marx's notes in anticipation of the writing The German Ideology, where he concludes with the banger "The philosophers have only interpreted the world, in various ways; the point is to change it."

But how then does human knowledge arise from practice and in turn serve practice? This will become clear if we look at the process of development of knowledge.

In the process of practice, man at first sees only the phenomenal side, the separate aspects, the external relations of things. For instance, some people from outside come to Yenan on a tour of observation. In the first day or two, they see its topography, streets and houses; they meet many people, attend banquets, evening parties and mass meetings, hear talk of various kinds and read various documents, all these being the phenomena, the separate aspects and the external relations of things. This is called the perceptual stage of cognition, namely, the stage of sense perceptions and impressions. That is, these particular things in Yenan act on the sense organs of the members of the observation group, evoke sense perceptions and give rise in their brains to many impressions together with a rough sketch of the external relations among these impressions: this is the first stage of cognition. At this stage, man cannot as yet form concepts, which are deeper, or draw logical conclusions.

As social practice continues, things that give rise to man's sense perceptions and impressions in the course of his practice are repeated many times; then a sudden change (leap) takes place in the brain in the process of cognition, and concepts are formed. Concepts are no longer the phenomena, the separate aspects and the external relations of things; they grasp the essence, the totality and the internal relations of things. Between concepts and sense perceptions there is not only a quantitative but also a qualitative difference. Proceeding further, by means of judgement and inference one is able to draw logical conclusions. San Kuo Yen Yi (Tales of the Three Kingdoms) is a famous Chinese historical nova by Lo Kuan-chung (late 14th and early 15th century).The expression in San Kuo Yen Yi, "knit the brows and a stratagem comes to mind", or in everyday language, "let me think it over", refers to man's use of concepts in the brain to form judgements and inferences. This is the second stage of cognition. When the members of the observation group have collected various data and, what is more, have "thought them over", they are able to arrive at the judgement that "the Communist Party's policy of the National United Front Against Japan is thorough, sincere and genuine". Having made this judgement, they can, if they too are genuine about uniting to save the nation, go a step further and draw the following conclusion, "The National United Front Against Japan can succeed." This stage of conception, judgement and inference is the more important stage in the entire process of knowing a thing; it is the stage of rational knowledge. The real task of knowing is, through perception, to arrive at thought, to arrive step by step at the comprehension of the internal contradictions of objective things, of their laws and of the internal relations between one process and another, that is, to arrive at logical knowledge. To repeat, logical knowledge differs from perceptual knowledge in that perceptual knowledge pertains to the separate aspects, the phenomena and the external relations of things, whereas logical knowledge takes a big stride forward to reach the totality, the essence and the internal relations of things and discloses the inner contradictions in the surrounding world. Therefore, logical knowledge is capable of grasping the development of the surrounding world in its totality, in the internal relations of all its aspects.

This dialectical-materialist theory of the process of development of knowledge, basing itself on practice and proceeding from the shallower to the deeper, was never worked out by anybody before the rise of Marxism. Marxist materialism solved this problem correctly for the first time, pointing out both materialistically and dialectically the deepening movement of cognition, the movement by which man in society progresses from perceptual knowledge to logical knowledge in his complex, constantly recurring practice of production and class struggle. Lenin said, "The abstraction of matter, of a law of nature, the abstraction of value, etc., in short, all scientific (correct, serious, not absurd) abstractions reflect nature more deeply, truly and completely." Marxism-Leninism holds that each of the two stages in the process of cognition has its own characteristics, with knowledge manifesting itself as perceptual at the lower stage and logical at the higher stage, but that both are stages in an integrated process of cognition. The perceptual and the rational are qualitatively different, but are not divorced from each other; they are unified on the basis of practice. Our practice proves that what is perceived cannot at once be comprehended and that only what is comprehended can be more deeply perceived. Perception only solves the problem of phenomena; theory alone can solve the problem of essence. The solving of both these problems is not separable in the slightest degree from practice. Whoever wants to know a thing has no way of doing so except by coming into contact with it, that is, by living (practicing) in its environment. In feudal society it was impossible to know the laws of capitalist society in advance because capitalism had not yet emerged, the relevant practice was lacking. Marxism could be the product only of capitalist society. Marx, in the era of laissez-faire capitalism, could not concretely know certain laws peculiar to the era of imperialism beforehand, because imperialism, the last stage of capitalism, had not yet emerged and the relevant practice was lacking; only Lenin and Stalin could undertake this task. Leaving aside their genius, the reason why Marx, Engels, Lenin and Stalin could work out their theories was mainly that they personally took part in the practice of the class struggle and the scientific experimentation of their time; lacking this condition, no genius could have succeeded. The saying, "without stepping outside his gate the scholar knows all the wide world's affairs", was mere empty talk in past times when technology was undeveloped. Even though this saying can be valid in the present age of developed technology, the people with real personal knowledge are those engaged in practice the wide world over. And it is only when these people have come to "know" through their practice and when their knowledge has reached him through writing and technical media that the "scholar" can indirectly "know all the wide world's affairs". If you want to know a certain thing or a certain class of things directly, you must personally participate in the practical struggle to change reality, to change that thing or class of things, for only thus can you come into contact with them as phenomena; only through personal participation in the practical struggle to change reality can you uncover the essence of that thing or class of things and comprehend them. This is the path to knowledge which every man actually travels, though some people, deliberately distorting matters, argue to the contrary. The most ridiculous person in the world is the "know all" who picks up a smattering of hearsay knowledge and proclaims himself "the world's Number One authority"; this merely shows that he has not taken a proper measure of himself. Knowledge is a matter of science, and no dishonesty or conceit whatsoever is permissible. What is required is definitely the reverse—honesty and modesty. If you want knowledge, you must take part in the practice of changing reality. If you want to know the taste of a pear, you must change the pear by eating it yourself. If you want to know the structure and properties of the atom, you must make physical and chemical experiments to change the state of the atom. If you want to know the theory and methods of revolution, you must take part in revolution. All genuine knowledge originates in direct experience. But one cannot have direct experience of everything; as a matter of fact, most of our knowledge comes from indirect experience, for example, all knowledge from past times and foreign lands. To our ancestors and to foreigners, such knowledge was—or is—a matter of direct experience, and this knowledge is reliable if in the course of their direct experience the requirement of "scientific abstraction", spoken of by Lenin, was—or is—fulfilled and objective reality scientifically reflected, otherwise it is not reliable. Hence a man's knowledge consists only of two parts, that which comes from direct experience and that which comes from indirect experience. Moreover, what is indirect experience for me is direct experience for other people. Consequently, considered as a whole, knowledge of any kind is inseparable from direct experience. All knowledge originates in perception of the objective external world through man's physical sense organs. Anyone who denies such perception, denies direct experience, or denies personal participation in the practice that changes reality, is not a materialist. That is why the "know-all" is ridiculous. There is an old Chinese saying, "How can you catch tiger cubs without entering the tiger's lair?" This saying holds true for man's practice and it also holds true for the theory of knowledge. There can be no knowledge apart from practice.

To make clear the dialectical-materialist movement of cognition arising on the basis of the practice which changes reality—to make clear the gradually deepening movement of cognition—a few additional concrete examples are given below.

In its knowledge of capitalist society, the proletariat was only in the perceptual stage of cognition in the first period of its practice, the period of machine-smashing and spontaneous struggle; it knew only some of the aspects and the external relations of the phenomena of capitalism. The proletariat was then still a "class-in-itself". But when it reached the second period of its practice, the period of conscious and organized economic and political struggles, the proletariat was able to comprehend the essence of capitalist society, the relations of exploitation between social classes and its own historical task; and it was able to do so because of its own practice and because of its experience of prolonged struggle, which Marx and Engels scientifically summed up in all its variety to create the theory of Marxism for the education of the proletariat. It was then that the proletariat became a "class-for-itself".

Similarly with the Chinese people's knowledge of imperialism. The first stage was one of superficial, perceptual knowledge, as shown in the indiscriminate anti-foreign struggles of the Movement of the Taiping Heavenly Kingdom, the Yi Ho Tuan Movement, and so on. It was only in the second stage that the Chinese people reached the stage of rational knowledge, saw the internal and external contradictions of imperialism and saw the essential truth that imperialism had allied itself with China's comprador and feudal classes to oppress and exploit the great masses of the Chinese people. This knowledge began about the time of the May 4th Movement of 1919.

Next, let us consider war. If those who lead a war lack experience of war, then at the initial stage they will not understand the profound laws pertaining to the directing of a specific war (such as our Agrarian Revolutionary War of the past decade). At the initial stage they will merely experience a good deal of fighting and, what is more, suffer many defeats. But this experience (the experience of battles won and especially of battles lost) enables them to comprehend the inner thread of the whole war, namely, the laws of that specific war, to understand its strategy and tactics, and consequently to direct the war with confidence. If, at such a moment, the command is turned over to an inexperienced person, then he too will have to suffer a number of defeats (gain experience) before he can comprehend the true laws of the war.

"I am not sure I can handle it." We often hear this remark when a comrade hesitates to accept an assignment. Why is he unsure of himself? Because he has no systematic understanding of the content and circumstances of the assignment, or because he has had little or no contact with such work, and so the laws governing it are beyond him. After a detailed analysis of the nature and circumstances of the assignment, he will feel more sure of himself and do it willingly. If he spends some time at the job and gains experience and if he is a person who is willing to look into matters with an open mind and not one who approaches problems subjectively, one-sidedly and superficially, then he can draw conclusions for himself as to how to go about the job and do it with much more courage. Only those who are subjective, one-sided and superficial in their approach to problems will smugly issue orders or directives the moment they arrive on the scene, without considering the circumstances, without viewing things in their totality (their history and their present state as a whole) and without getting to the essence of things (their nature and the internal relations between one thing and another). Such people are bound to trip and fall.

Thus it can be seen that the first step in the process of cognition is contact with the objects of the external world; this belongs to the stage of perception. The second step is to synthesize the data of perception by arranging and reconstructing them; this belongs to the stage of conception, judgement and inference. It is only when the data of perception are very rich (not fragmentary) and correspond to reality (are not illusory) that they can be the basis for forming correct concepts and theories.