Agreement between moral theories › The proposed route to convergence

One important route begins with Parfit's Kantian Contractualist Formula. This concerns principles whose universal acceptance everyone could rationally will or choose. Parfit then argues for a connection between that test and principles whose universal acceptance makes things go best. If the argument succeeds, a Kantian approach supports a form of rule consequentialism.

A further step connects those principles to reasonable rejection. Parfit argues that the relationship can bring a Scanlonian condition into the account. The argument needs to establish whether optimific principles are the only ones whose universal acceptance everyone could rationally choose, and whether they are the only principles no one could reasonably reject. These are propositions to defend, not definitions that make convergence automatic.

An analogy can clarify the ambition without serving as proof. Imagine two different tests of whether a bridge design is acceptable. One assesses how its parts bear loads; another evaluates how the whole structure behaves. Agreement on a few designs would be encouraging, but a claim that the tests are equivalent would require explaining their relationship. Moral tests involve contested reasons rather than engineering measurements, so the analogy reaches only as far as that distinction between matching examples and an argument for equivalence.

The same discipline applies to counterexamples. If a proposed formulation gives an implausible result, Parfit can revise it, but the revision needs a reason beyond making the convergence argument work. A reader can ask whether the new formulation improves the theory on its own terms. Otherwise, the procedure risks selecting definitions to secure the desired agreement.

This is why a short account should not present the book as a demonstration that every conflict between duties and outcomes is illusory. The argument concerns selected, developed formulations. A person who rejects one reformulation may retain a coherent disagreement with the proposed synthesis. Understanding exactly where the disagreement remains is a useful result of reading the argument.