The broad context is a discussion of priority and posteriority, which runs from 1018b9–1019a14 (compare Categories 14a26–b24). A type of priority is described at 1019a2–4, and then further discussed at 1019a4–14. It is described as follows: ‘All those things are said to be prior in respect of nature and being, which can exist without other things, while those other things cannot exist without them.’ My concern in this note is with the parenthesis which immediately follows: ‘This is a distinction which Plato employed.’

All the commentators despair of locating this reference to Plato. Some, like Tredennick, (ad loc. in his Loeb edition), simply despair; others, like Ross (ad loc. in his edition), speak of ‘an oral utterance’, and are accordingly tempted towards finding yet another reference to the Unwritten Doctrines, either in the vague sense that anything not in the dialogues is by definition ‘unwritten’, or more specifically in the sense of some aspect of the doctrine of ideal numbers (e.g. Trendelenburg, cited by Ross).