Aristotle takes a relation to hold between two objects, the relata . A relatum has its existence dependent upon the existence of its correlative relatum . Likewise defining a relation requires mentioning both relata : parenting is the begetting of one human being by another. Because of the need to specify the other relatum in the definition of the relation itself, a relatum has a unique kind of "conversion ": e.g., a parent is a parent of a child; a child is a child of a parent. Although Aristotle allows relata in ordinary, endoxic usage to come from other categories and to come to be at different times, strictly a relation is between relata only, which exist simultaneously. A wing may be the wing of a bird, but it is of "the bird qua winged". The relata are paronyms named from the relation . These relata have a quasi-independence from their base substances and can serve as logical subjects, or hypostases , in their own right. Yes, as these subjects have such a dependent existence, there is no danger of someone taking such abstract objects as substances in their own right. Like perception and knowledge, abstraction is a relation having all of these features.