Agreement between moral theories › What the Triple Theory says

In the 28 April 2008 author draft listed below, Parfit's Triple Theory says that an act is wrong just when acts of that kind are disallowed by principles that are optimific, uniquely universally willable, and not reasonably rejectable. In this context, an optimific principle belongs to principles whose relevant universal adoption would make things go best. Universal willability concerns what everyone could rationally will as universal laws. Non-rejectability supplies the contractualist condition.

The proposal is about principles with these properties, rather than a vote among three theories. It should not be paraphrased as saying an act is wrong only when three independent moral judges all disapprove. Such a voting procedure could leave disagreements unresolved without explaining why the theories agree. Parfit wants to defend a common account of the principles that govern conduct.

Each condition brings a substantive question. What makes outcomes better? Which reasons may someone use in deciding what they could rationally will? What makes rejecting a principle reasonable? The compact formula does not answer these questions merely by containing three technical terms. Much of the book's argument concerns how to understand them and whether their requirements can be brought together.

The uniqueness qualification matters too. If several incompatible sets of principles could each be rationally willed, the proposed route from rational willing to a particular moral standard would need further work. Identifying a principle that someone could accept is weaker than showing that everyone has the relevant reasons to choose that principle over its alternatives. Readers should watch these changes in logical strength.

Parfit's discussion also distinguishes principles that are universally accepted from principles that are universally followed. Acceptance concerns how people regard and use a principle; following concerns conduct that conforms to it. These descriptions can come apart. A person might accept a prohibition yet violate it. An argument about the consequences of universal acceptance must therefore avoid silently substituting the consequences of universal compliance.