Full Idea
The three most common objections to the constitution view are the Impenetrability Objection (two things in one place?), the Extensionality Objection (mereology says wholes are just their parts), and the Grounding Objection (their ground is the same).
Gist of Idea
There are three main objections to seeing constitution as different from identity
Source
Ryan Wasserman (Material Constitution [2009], 2)
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.7
A Reaction
[summary] He adds a fourth, that if two things can be in one place, why stop at two? [Among defenders of the Constitution View he lists Baker, Fine, Forbes, Koslicki, Kripke, Lowe, Oderberg, N.Salmon, Shoemaker, Simons and Yablo.]
Related Idea
Idea 16067 Constitution is not identity, because it is an asymmetric dependence relation [Wasserman]