This paper presents an implemented hybrid approach to grammar and style checking, combining an industrial patternbased grammar and style checker with bidirectional, large-scale HPSG grammars for German and English. Under this approach, deep processing is applied selectively based on the error hypotheses of a shallow system. We have conducted a comparative evaluation of the two components, supporting an integration scenario where the shallow system is best used for error detection, whereas the HPSG grammars add error correction for both grammar and controlled language style errors.