Let us call the Modal Argument against the Identity Thesis MAIT.

Charles Taylor has recently argued that defenders of the identitythesis commonly omit any argument that general identities could beestablished on the basis of any future scientific research, and thatunless such identities could be established, the truth of the identitythesis would be deprived of an important source of interest. [Taylor(1)]

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We will spell out the argument first. Next, we will need to detour through another point due to Kripke - which we can call the "Strengthening of Identity". This latter claim furnishes one of the premises of the argument against the Identity Thesis (IT).

TheIdentityTheory accepts both of the following:

Suppose that the types  and are identical (this is what the type identity theory maintains)�

If the notion is interpreted in this way then the relation betweenthe criterion of identity and the criterion of application will be thatof one-way determination. The criterion of identity will be determinedby, but not determine, the criterion of application.