The theory of frames has recently been proposed as a universal format for knowledge representation in language, cognition and science. Frames represent categories as well as individual objects and events in terms of recursive attribute-value structures. In this paper, we would like to explore the potential ontological commitments of frame-based knowledge representations, with particular emphasis on the ontological status of the possessors of quality attributes in individual object frames. While not strictly incompatible with nominalistic, bundle- or substratum-theoretic approaches to the (...) metaphysics of particular objects, it will be argued that representing objects in terms of attribute-value structures is more in accordance with a tradition that can be traced back to Aristotle’s doctrine of physical substances. Attributes appear to describe primary potentialities of objects, which, in the Aristotelian view, are the unchangeable nature or essence, hence substance, of any separate object. (shrink)