ABSTRACT
Processability Theory (PT) is a theory of second language (L2) development. The core of PT is formed by a universal processability hierarchy that is based on W. J. M. Levelt’s approach to language production. The processability hierarchy is based on the notion of transfer of grammatical information within and between the phrases of a sentence. Processability affects first language (L1) and L2 development and also constrains interlanguage variation and L1 transfer. The learner of a language needs to develop procedures that can handle the job of storing and comparing grammatical information. The fact that learners have no choice in the path they take in the development of processing procedures follows from the time course of language generation and the design of the processing procedures. Functional structure consists of universal grammatical functions that are related to constituent structure in a language-specific way.
