Abstract
In order to develop the ontology of tendencies for use in the representation of medical knowledge, tendencies are compared with other kinds of entities possessing the realizable-realization structure, specifically: dispositions, propensities, abilities and virtues. The peculiarities of tendencies are discussed and a standard schema of tendency ascription is developed in order to represent the relations between the ascriptions of tendency tokens to particulars and the ascriptions of tendency types to universals. Two nonstandard cases and their epistemic variants are discussed.