Man’s social practice is not confined to activity in production, but has taken many other forms – class struggle, political life, scientific pursuits;[3-290] in short, as a social being, man participates in all spheres of the practical life of society. Thus man[3-291] comes to understand[3-292] the different and complex 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; and this is because, in class society,[3-293]every kind of thinking, without exception, is stamped with the brand of a class.[3-294]
Because of this, 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 strengthened[3-295] only when he achieves the anticipated results in the process of social practice (material production, class struggle or scientific experiment). Why is it that peasants are unable to harvest their crops, that workers are unable to use their tools, that there are strikes and struggle, that troops go to war, and that the national revolution has not achieved victory? It is because man’s knowledge has not faithfully reflected the regularities
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, on the first day or two in Yan’an, a Guomindang inspection team[3-300] sees 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. That is called the perceptual stage of cognition, namely, the stage of sense perceptions and impressions. That is, these particular things in Yan’an 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 theoretical conclusions.[3-301]