The overall reflection of human thinking on the nature of objective things. Each discipline has its own basic category. Such as contradiction in philosophy, quality and quantity, essence and phenomenon, commodity value, abstract labor, concrete labor, chemical combination and decomposition in political economy, etc. Category, as a mathematical concept, is an algebraic structure, including arrows between objects. Category has two basic properties: first, arrows between objects can be combined, and the combination satisfies the law of association; Second, each object has its own unit arrow. A simple category example is that an object consists of sets, and the mapping between sets is regarded as an arrow. Generally speaking, objects and arrows can be of any abstract type, and the concept of category provides a basic and abstract method to study objects and their relationships in mathematics. Category is an auxiliary concept, and each category is an artificially created and organized term. It provides a classification style for science, acts as a tool of thinking technology, defines the framework of discussion and brings a sense of theme. Talented writers are always good at mobilizing readers' imagination to the maximum extent, allowing them to re-experience the thoughts and feelings experienced by writers themselves and rebuild their artistic image in their ideas. The indirectness, ideality and imagination of literary image make it not as direct as painting, sculpture, drama and film image, but it also has advantages that other arts do not have. The language used to construct literary images is the most "soft", flexible, plastic and convenient to use. It has the ability to travel through time and space, and can "penetrate" all tangible or intangible things.