This article surveys corpus research into what might generally be referred to as conventionalism in language use, and discusses its implications for second language teaching methodology. After an introductory section with traditional and more recent views on the idiomatic and formulaic nature of language use, Section 2 presents a survey of corpus-based case studies into preselected types of lexical patterning like idioms and collocations. Section 3 presents the cruder statistical approach of automatically assessing the frequency of recurrent combinations in texts. The results suggest that conventionalism extends far beyond the traditionally recognised patterns, and might be the basic combinatory principle underlying the composition of written and oral texts. After a short section with some evidence that conventional sequencing is also a feature in learner output, the concluding section (5) argues that to do justice to the phenomenon of conventionalism in language use, teaching methodology should be essentially text-based.
