Languages do not occur in static or stable states. All languages exhibit some degree of grammatical variation, and they change over time; in fact, much synchronic variation represents language change in progress. Changes in linguistic structure are changes in the grammatical properties that enter into one or more of the cross-linguistic patterns described in the preceding chapters. This fact suggests two extensions of typology. First, if language types fall into universal cross-linguistic patterns, then it is worth investigating if the cross-linguistic patterns also govern changes in language type. Second, it should be possible to classify typologically the linguistic changes themselves, and look for relationships among linguistic processes in the same way that typologists seek relationships among linguistic states. This latter process has been especially fruitful and has led to intensive study of a family of associated language processes called grammaticalization.

The dynamicization of synchronic typology

We may return to the foundations of synchronic typology in order to see its consequences for language change. Synchronic typology is founded on the typological classification of logically possible linguistic types (chapter 2). Once this is established, one then constructs a language sample in order to determine which of the logically possible language types are actually attested in the languages of the world, and formulates universals (implicational universals, typological markedness, prototypes, conceptual distance, formal complexity, etc.) that restrict human languages to the actually occurring types. These universals are then explained in external terms.