PM concerns the learnability and teachability of an L2’s language structures. Its driving force was Manfred Pienemann, a German psychologist, formerly of the University of Sydney and now at Newcastle University.
PM’s basic idea is that since all learners seem to acquire language in a predictable order, there’s little point in teaching a language structure to learners if they’re not ready to acquire it. Hence Pienemann’s ‘teachability hypothesis’:
An L2 structure can be learnt from instruction only if the learner’s interlanguage is close to the point when this structure is acquired in a natural setting.
In other words, there’s no point teaching the third person present form to early learners since they’re not ready to acquire it.
Pienemann proposed that there were six stages through which L2 learners went:
Stage 1: learners use single words or single (prefabricated) chunks (e.g. what’s the time?)
Stage 2: learners acquire SVO word order (e.g. I eat bread, you have cat?)
Stage 3: Learners start to add bits to the start and end of SVO sentences, such as adverbials (e.g. On Tuesday I watch TV) and wh- questions (e.g. where the cats are?)
Stage 4: learners start to move prepositions and use the -ing ending (e.g. I am reading a book); they can form yes/no questions requiring inversion (e.g. have you got a cat?)
Stage 5: learners start to form wh- questions using inversion (e.g. where does your cat sit?) and the third person ‘s’ (e.g. he likes); they also start using the ‘to’ preposition (e.g. he gives the ball to the girl). At this stage, learners can work within a sentence, inserting words and moving them around rather than just adding them to the start and end of sentences.
Stage 6: learners form ‘can’ questions using inversion (e.g. can you see what the time is?) and can make use of subordinate clauses.
To back up his theory, Pienemann studied ten Italian children aged between 7 and 9 who were learning German. All the children were given language instruction at the same stage; some children were at the preceding stage, while the remainder were at an earlier stage. Pienemann found that only the children at the preceding stage learned the instructional target.
This has considerable implications for teaching and the design of syllabuses. Supported by large numbers of other studies, it seems that you cannot get learners to learn structures that are beyond their developmental stage. Learning is constrained by current language knowledge…although it must be said that a lot of Pienemann’s work concerns word order and question formation.
Textbook-based courses typically pay no heed to acquisition orders, introducing different verb tenses one after the other and introducing questions early on…well before learners are ready to acquire these forms (however, exposing learners to these forms might make acquisition easier later on).
Pienemann (1984): Psychological Constraints on the Teachability of Languages
Pienemann (1989): Is Language Teachable?
Pienemann (2005): An Introduction to Processability Theory (Chapter 1 of Cross-Linguistic Aspects of Processability Theory)