And it must be remembered that Hebrew had been continuously used in liturgical and legal contexts, and had been routinely taught to Jewish males during its 1700 year-long coma, so it was never entirely dead. Documented profiles of languages, whether alive or dead, are valuable to cultural historians and anthropologists, to theoretical linguists, to psychologists, philosophers, and many other kinds of scholars. Each language contains clues about the history of a people. Hypotheses about migration patterns can be supported by seeing whether words have been assimilated from the languages of neighbouring populations. The syntax of a language is a guide to its evolutionary descent too.
Linguists glean a lot from comparing the syntactical rules of different languages.
For example, Chomsky's well- known hypothesis that all human languages conform to an innately specified general pattern which he called 'Universal Grammar' is supposed to be an empirical hypothesis. Evidence from a wide variety of languages is essential in order to test it properly. For all we know, some language exists which disconfirms Chomsky's hypothesis. But if X died out without being documented, we would never know if X was a counterexample or not. Cognitive psychologists devise models of speech- production and understanding in which specific assumptions are made about representations, levels of representation, and processing.