Pienemann's Processability Theory is an interesting and well thought out attempt to account for the developmental problem in L1 and L2. If correct, it would relieve the genetically specified knowledge base of what he views as its burdensome task of having to specify a great deal of genetically encoded linguistic knowledge and transfer at least part of that task to the processing mechanisms available for the acquisition of procedural skills needed for language processing. He posits a set of processing resources forming an implicational hierarchy such that the resource of a certain level is a prerequisite for the functioning of the next higher level. He posits further that the processing devices will be acquired in their predetermined sequence of activation in the production process. A consequence of this is that acquirers of both the first and the second language will follow the same sequence of acquisition of the processing hierarchy. The differences in the courses of development can be attributed, he says, to the knowledge base with which the learner comes to the acquisition task. In the case of L1, he says, many would see UG as the knowledge base; in the case of L2, only the surface syntactic features of the target language are available (and, presumably, knowledge of the L1).