A barrier to entailment exists if you can't get conclusions of a certain kind from premises of another. One of the most famous barriers in philosophy is Hume's Law, which says that you can't get normative conclusions from descriptive premises, or in slogan form: you can't get an ought from an is. This barrier is highly controversial, and many famous counterexamples were proposed in the last century. But there are other barriers which function almost as philosophical platitudes: no Universal conclusions from Particular premises, no Future conclusions from premises about the Past, and no claims that attribute Necessity from premises that merely tell us how things happen to be in the Actual world. Barriers to Entailment proposes a unified logical account of five barriers that have played important roles in philosophy, in the process showing how to diagnose proposed counterexamples and arguing that the case for Hume's Law is as strong as that for the platitudinous barriers. The first two
