THIS BOOK IS ABOUT LEARNING a second language. It would be
a rare person who is unfamiliar with this experience, whether success-
ful at it or not. People encounter this experience in numerous ways:
as a student, as a tourist, as an immigrant. What are the essential
characteristics of learning a second language? Why is it easier for
some people than for others? Are there times or situations in which
the process becomes easier? These are the kinds of questions language
learners inevitably ask and the kinds of issues that commonsense, or
folk theories of language learning, attempt to address.

This book is also about our efforts to understand second-language
learning and the methods we use to come to that knowledge. Schol-
ars have long puzzled over the mysteries of language learning, and
researchers have explored numerous aspects of its development.
These academic approaches to language learning have originated in a
variety of disciplines--linguistics, biology, psychology, anthropol-
ogy, and sociology; each of these lays some claim to understanding
the process. But what are the differences in the approaches taken by
these disciplines? How do their insights fit together to reveal some-
thing more general or more essential about the process of second-
language learning?

We expect that most readers will be interested in knowing more
about second-language learning from the point of view of both per-

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