This book began with a mystery. I had been reading about formulaic language in the context of language proficiency, and had been struck by three observations made in the literature. The first was that native speakers seem to find formulaic (that is, prefabricated) language an easy option in their processing and/or communication. The second was that in the early stages of first and second language acquisition, learners rely heavily on formulaic language to get themselves started. The third observation, however, seemed to fly in the face of the first two. For L2 learners of intermediate and advanced proficiency, the formulaic language was the biggest stumbling block to sounding nativelike. How could something that was so easy when you began with a language, and so easy when you were fully proficient in it, be so difficult in between?

I set myself the challenge of finding out, and focussed on two possibilities, both of which I now judge to be true. One was that the formulaic language described in the various areas of study was not quite the same thing in each case. The second was that there was some other key to understanding the nature of formulaic language, one which would be difficult to spot by looking only at the different types of data in isolation. The common link between formulaic language across different speakers might even not be linguistic at all.