This paper will look at some grammatical phenomena which will illustrate some of the questions that can be addressed with a corpus-based approach. We will use this approach to investigate the following subjects in English grammar: number ambiguity, subject-verb concord, concord with measure expressions, and (reflexive) pronoun choice in coordinated noun phrases. We will emphasize the distinctive features of the corpus-based approach, particularly its strengths in investigating language use, as opposed to traditional descriptions or prescriptions of structure in English grammar. This paper will show that a corpus-based approach has made it possible to conduct new kinds of investigations into grammar in use and to expand the scope of earlier investigations. Native speakers rarely have accurate information about frequency of use. A large representative corpus (i.e., The British National Corpus) is one of the most reliable sources of frequency information. It is important to base an analysis of language on real data rather than intuition. Any description of grammar is more complete and accurate if it is based on a body of real data.