Languages: A Very Short Introduction

Anderson, Stephen R., and Stephen Anderson. Languages: A Very Short Introduction. Vol. 320. New York: Oxford University Press, 2012.

Chapter 3

Language divergence (phylogenetic). With time changes, 20 or 30 years, local differences would have emerged, such as local accents because new words and expressions limited to particular places. 

The regularity of linguistic change: sound change. Grimm's Law: 

a. voiceless stops became voiceless fricatives (e.g., [p]>[f]);

b. voiced stops became voiceless (e.g. [b]>[p]); and

c. voiced aspirates became simple voiced stops (e.g. [bh]>[b]). 

Chapter 4

A language's survival is the extent to which new generations are learning it. (chap.4)

"As soon as the language is lost, an essential link to the group's history and cultural patrimony is cut." (chap.4)

Chapter 6

How is the number of languages in the world?  Counting by I-language. We should distinguish I-language (internal) and E-language (external). I-language "refers to that aspect of a speaker's cognitive organization by virtue of which we say that she 'speaks' or 'knows' the language in question." In other words, we can count the range of distinct grammars in the world.

Chapter 8

"There is a single biologically based capacity for language that is essentially uniform across our species, but which develops in different ways in different individuals depending on their specific environment and experiences."