Full Idea
Mereologists do suppose that constitution is a criterion of identity. This view is enshrined in the Mereological axiom of extensionality; that objects with the same parts are identical.
Gist of Idea
Mereology treats constitution as a criterion of identity, as shown in the axiom of extensionality
Source
Verity Harte (Plato on Parts and Wholes [2002], 3.1)
Book Reference
Harte,Verity: 'Plato on Parts and Wholes' [OUP 2002], p.121
A Reaction
A helpful explanation of why classical mereology is a very confused view of the world. It is at least obvious that a long wall and a house are different things, even if built of identical bricks.