Meaning of external relation

exter'nal rela'tion

Pronunciation: [key]
— Philos. Philos.
  1. a relation between any two entities such that if they had not been in this relation to each other, the nature of each would not necessarily have been different. Cf. internal relation.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.