Abstract:  This talk is going to be an introduction to my book project on barriers to entailment. The book is about barrier theses, which are theses which say that no set of premises containing only sentences of a certain kind, X, logically entails a conclusion of some other kind, Y. More colloquially, barrier theses say that you can’t get an X from a Y. Hume’s Law is an example; it says that no set of merely descriptive sentences entails a normative one, or (in slogan form):  you can’t get an ought from an is.   Other barrier theses that have been important in philosophy include:  you can’t get universal claims from particular ones;  you can’t get claims about the future from claims about the past; you can’t get claims about how things must be from claims about how things are; and you can’t get indexical claims from claims which are not context-sensitive.