Full Idea
An essential part of an essential part is an essential part of the whole.
Gist of Idea
An essential part of an essential part is an essential part of the whole
Source
Peter Simons (Parts [1987], 7.4)
Book Reference
Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.271
A Reaction
Sounds beyond dispute, but worth pondering. It seems to be only type-parts, not token-parts, which are essential. Simons is thinking of identity rather than function, but he rejects Chisholm's idea that all parts are essential. So which ones are?