Full Idea
The notion of change is obscured by the doctrine of substance, by a thing's nature versus its external relations, and by subject-predicate form, so that things can be different and the same. Hence the useless distinction between essential and accidental.
Gist of Idea
Change is obscured by substance, a thing's nature, subject-predicate form, and by essences
Source
Bertrand Russell (The Principles of Mathematics [1903], §443)
Book Reference
Russell,Bertrand: 'Principles of Mathematics' [Routledge 1992], p.471
A Reaction
He goes on to object to vague unconscious usage of 'essence' by modern thinkers, but allows (teasingly) that medieval thinkers may have been precise about it. It is a fact, in common life, that things can change and be the same. Explain it!