Deutscher's approach to linguistic change was all new to me and quite fascinating. It is a given that people writing about their own language at every point of recorded history bemoan the fact that in modern days it's not spoken or written as well as it used to be; also linguistic reconstructions of extinct languages always seem to generate the impression that they were better ordered and more complex than their descendants today. Yet we also see new linguistic structures developing at the same time - he looks for instance at the future tense in French, at the use of "gonna" and "got" in English, and in considerable depth at the historical development of tense markers in Semitic verbs - mainly Arabic, but also Hebrew which has changed a lot in only the last century. In the end he makes a very good case that there is basically an equilibrium between language speakers unconsciously eroding old grammatical structures out of sheer laziness, but then being compelled to invent new elements to cover nuances of meaning that are needed - and these new elements emerge only gradually, so that "going to" shifts quite imperceptibly from only indicating movement to becoming an equivalent marker for "shall/will".
This was voted top of the non-fiction section of my 2014 unread books poll by you guys. Good call.