Foreign language learners are commonly taught explicit rules of grammar, but often fail to apply them when confronted with communicative tasks. How well ha ve they learnt the rules? Do they recognize where they are to be applied? A re they better at some rules than others? Above all, how is getting the language right related to explicit rule knowledge? Twelve errors commonly committed by German pupils performing com-municative tasks in English were put before 300 German learners of English at different levels. They were asked to state the rules they believed had been trans-gressed and to correct the errors. A peer group of 50 native speakers of English was given the same test. The learners' ability to state relevant rules and supply appropriate corrections for the errors is examined with reference to some of the assumptions and expectations that lie behind explicit grammar teaching.