Linguistic theory in the modern sense has received its impetus from the seminal work done within the framework of generative grammar since the mid 1950's. A good theory should exhibit at least four basic properties 1) economy, 2) simplicity, 3) generality, 4) falsifiability. Furthermore a theory must be adequate on three levels: that of observation, of description and of explanation.

• Different levels of language have been subject to theories in the second half of the 20th century. In particular, phonology and syntax, because of their abstract and formal properties, have attracted linguists of a theoretical persuasion. There is no generally accepted theory of semantics because the data is somewhat too diffuse and fuzzy-edged. And as regards morphology one can note that it is usually treated as subordinate to syntax (at least in generative theories).