Categories of the understanding

In Kant's philosophy, a category (German: Categorie in the original or Kategorie in modern German) is a pure concept of the understanding (Verstand). A Kantian category is a characteristic of the appearance of any object in general, before it has been experienced. Kant wrote that "They are concepts of an object in general…." Kant also wrote that, "…pure cоncepts [Categories] of the undеrstanding…apply to objects of intuition in general…." Such a category is not a classificatory division, as the word is commonly used. It is, instead, the condition of the possibility of objects in general, that is, objects as such, any and all objects, not specific objects in particular.

The word comes from the Greek , katēgoria, meaning "that which can be said, predicated, or publicly declared and asserted, about something." A category is an attribute, property, quality, or characteristic that can be predicated of a thing. "…I remark concerning the categories…that their logical employment consists in their use as predicates of objects." Kant called them "ontological predicates."

Aristotle had claimed that the following ten predicates or categories could be asserted of anything in general: substance, quantity, quality, relation, action, affection (passivity), place, time (date), position, and state.

These are supposed to be the qualities or attributes that can be affirmed of each and every thing in experience. Any particular object that exists in thought must have been able to have the Categories attributed to it as possible predicates because the Categories are the properties, qualities, or characteristics of any possible object in general. The Categories of Aristotle and Kant are the general properties that belong to all things without expressing the peculiar nature of any particular thing. Kant appreciated Aristotle's effort, but said that his table was imperfect because " … as he had no guiding principle, he merely picked them up as they occurred to him..."

The Categories do not provide knowledge of individual, particular objects. Any object, however, must have Categories as its characteristics if it is to be an object of experience. It is presupposed or assumed that anything that is a specific object must possess Categories as its properties because Categories are predicates of an object in general. An object in general does not have all of the Categories as predicates at one time. For example, a general object cannot have the qualitative Categories of reality and negation at the same time. Similarly, an object in general cannot have both unity and plurality as quantitative predicates at once. The Categories of Modality exclude each other. Therefore, a general object cannot simultaneously have the Categories of possibility/impossibility and existence/non–existence as qualities.

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