J. H. Greenberg was the founder of the Functionalist school of linguistics. As such, he played a somewhat parallel role to that of Noam Chomsky for the Generative school. This book was one of the earliest attempts to set out a listing of linguistic "Universals" -- rules which hold true for all or almost all languages having a certain, different property. So, if a language is such that the subject precedes the Object, and that both precede the verb, then that language will overwhelmingly be one which had postfixes, instead of prefixes. Greenberg himself settled for around 50 such Universals. If you want an up-to-date list of Universals, go to the web site of the Linguistics Archive of the University of Konstanz, where you will find a list of over 2,000 Universals. But, Greenberg is the one who got this industry in Linguistics moving.