A permanent concern of philosophers has been to discover whether the most general categories of thought, such as space, time, reality, existence, necessity, substance, property, mind, matter, states, facts, and events, are absolute and universal, to be found in any mode of thought, or whether they are relatively parochial and in principle changeable. In the Categories and the Topics Aristotle lists ten categories: substance, quantity, quality, relation, place, time, posture, state, action, and passion, but he seems not to have been wedded to the idea that this classification was definitive. He held that any ‘uncombined’ term in a sentence stands for one of these (see also paronym). Other terms are auxiliary terms, later called syncategorematic expressions or ones that together with categorical expressions make up a sentence. These include prepositions and logical connectives. In scholastic thought Aristotle’s list becomes substance, quantity (the way a body is made up of others, and owes its extension to theirs), the acting and being acted upon of a body (its activity and passivity), qualities arising from the disposition of constitutive parts, spatial and temporal properties, and relations.

Kant’s passion for system led him to a fourfold division with three categories in each. Under quantity we have unity, plurality, and totality; under quality we get reality, negation, and limitation; under relation we have inherence and subsistence, causation and dependence, and reciprocity between agent and patient; under modality we have possibility, existence, and necessity. Few have had Kant’s faith that this is an exhaustive and principled division. In the modern era Frege’s logic gives us a clearer view of the fundamental ways in which information is constructed, and his analysis of language suggests the highly general division of concept and object, but by itself it does not speak to the problems of classification within these categories. A new twist was added by Wittgenstein’s Tractatus Logico-Philosophicus (1921) in which it is suggested that the fundamental categories of a language show themselves, but their structure and relations are amongst the things that cannot be said. The problem remains of finding a fundamental classification of the kinds of entities recognized in a way of thinking. See also disposition.