I recently bought a book that begins with a foreword, a preface, and an introduction (in that order). The introduction was the only one written by the main author of the book; the other two were written by celebrities who had nothing else to do with the book. My question is what is the difference between a foreword, a preface, and an introduction?
Welcome to EL&U! I am not sure if this question relates specifically to the language and usage of English. Nonetheless, here are the differences:
A foreword is written by a person other than the author, usually an expert in the field, most often as a means of adding ethos to the author's book. This adds to the author's credibility. For example, in the book 'A Brief History of Time' by Stephen Hawking, the foreword was written by Carl Sagan, a renowned astrophysicist and expert that promoted the book.
The difference between preface and introduction is a fine one. While the preface provides context about the composition of the book, the introduction provides context about the content of the book. This means that the preface gives information such as how the author came to write the book, why it was worthy of writing, etc. The introduction gives precursory information to the contents of the book. A book on quantum physics, for example, might give some historical information on developments in the field.
I hope this is useful.