Publication Date



Open access

Embargo Period


Degree Type


Degree Name

Doctor of Philosophy (PHD)


Philosophy (Arts and Sciences)

Date of Defense


First Committee Member

Otávio Bueno

Second Committee Member

Amie L. Thomasson

Third Committee Member

Elijah Chudnoff

Fourth Committee Member

Berit Brogaard

Fifth Committee Member

Daniel Nolan


In this dissertation, I develop an account of non-vacuous counterpossibles—counterfactuals involving metaphysical impossibilities—and related notions, e.g. metaphysical similarity between impossible worlds, that does not require us to take on questionable ontological commitments and that gives us a clear epistemological story about how we know counterpossible claims. My account of counterpossibles builds on a non-descriptivist account of metaphysical modality called modal normativism, which has been developed by Amie Thomasson. According to modal normativism, claims of metaphysical necessity and possibility are not descriptive claims in need of modal truthmakers, but instead serve the normative function of enabling language users to illustrate or express constitutive rules that govern the use of ordinary non-modal vocabulary but while staying in the object language using, rather than mentioning, the terms. Roughly, on my account, the evaluation of metaphysical counterpossibles only requires us to tacitly consider how the actual rules that govern the use of our terms are changed in a deviant, yet relevantly similar, linguistic framework that accommodates the description of some hypothetical impossible scenario. After presenting my view, I respond to two general worries one might have about my account. Finally, I offer a sketch of two easy ways to think about impossible worlds for those who might feel uncomfortable adopting such talk.


impossible worlds; counterpossibles; modal normativism; metaphysical laws; conceptual engineering; modality; metaphysics