Full Idea
'Composition as identity' says that when a thing, x, is composed of some other objects, the ys, then this is a kind of identity between the x and the ys. The industrial-strength version says object x just is the ys. Lewis says it is just an analogy.
Gist of Idea
'Composition as identity' says that an object just is the objects which compose it
Source
Theodore Sider (Four Dimensionalism [2001], 5.3)
Book Reference
Sider,Theodore: 'Four Dimensionalism' [OUP 2003], p.159
A Reaction
I am averse to such a doctrine, as is Leibniz, with his insistence that an aggregate is not a unity. There has to be some sort of principle that bestows oneness on a many. I take this to be structural, and is an elucidation of hylomorphism.