The first foreign language I learned to complete fluency was German - after five years of high school German I spent a year at a German boys' boarding school. At the end of that year I was completely fluent, but noticed an odd phenomenon, that I felt like a slightly different person when I spoke German than when speaking English. Since then I've also learned Spanish to a high degree of fluency, and the same observation holds. In both cases, the main difference that I perceive has to do with humor, and the way the language I'm speaking affects my sense of humor. So I've always been interested in the extent to which language affects thought. The notion that it does is what linguists refer to as the Sapir-Whorf hypothesis. Belief in Sapir-Whorf reached its peak in the first half of the 20th century, but since then the notion that language affects cognition has been discredited by almost all mainstream linguists.
In "Through the Language Glass" Guy Deutscher mounts a careful, very limited defence of the Sapir-Whorf hypothesis. He considers three major areas - the link between language and color perception, how different languages deal with spatial orientation, and the phenomenon of differences in noun genders across different languages. His examination of the link between language and color perception is extensive and thought-provoking - he traces the development of linguistic theory on color perception from British prime minister Gladstone's commentary on the relative paucity of color terms in Homer's work, through the Berlin-Kay model (stating essentially that languages all tend to split up the color spectrum in similar ways) through very recent experiments suggesting that the existence of a particular color distinction in a language (e.g. the existence of separate terms in Russian for light and dark blue) affects the brain's ability to perceive that distinction. Deutscher's account of the evolution of linguistic theory about color perception is a tour de force of scientific writing for a general audience - it is both crystal clear and a pleasure to read.
Two factors contributed to my eventual disappointment with this book. The first is that, even after Deutscher's careful, eloquent, persuasive analysis, one's final reaction has to be a regretful "So what?" In the end, it all seems to amount to little of practical importance.
The second disappointment pertained only to the experience of reading this book on an Amazon Kindle. Reference is made throughout to a "color insert" which evidently contained several color wheels as well as up to a dozen color illustrations. This feature was completely absent from the Kindle edition, which had a severe adverse effect on the overall experience of reading this book. Obviously, this point is relevant only if you are contemplating reading the Kindle version - DON'T!
If it hadn't been for the lack of availability of key illustrations on the Kindle, I would have given the book 4 stars, but I feel obliged to deduct one because of the Kindle-related deficiencies.