On the basis of a critical analysis of the articles in this issue, we argue for a shift in emphasis in the investigation of universals in second language acquisition (SLA). To construct a psycholinguistically plausible theory of acquisition, research must proceed simultaneously on a number of different fronts: the elaboration of (a) a theory of computation consistent with human biology, (b) a theory of structural universals and variation, (c) a theory of meaning, and (d) a theory of pragmatics which must tie in with both a theory of cognitive development and a theory of sociocultural knowledge. None of the theories popular at present address all of these issues. We suggest that there is much room for consensus, but that achieving it will require keeping an eye firmly focused on the long-term objectives.

To the extent that language universals represent internal properties of human beings, one would expect them to manifest themselves in first language (L1) acquisition. Whether they should also manifest themselves in second language (L2) acquisition depends on whether or not language universals remain accessible to adults. The relation between L2 acquisition and language universals research is examined with respect to three phenomena: extraction, where the subset principle makes interesting predictions, although the second language data are far from clear; structure dependence, where there is evidence for the continuation beyond puberty of a general formal property of language; and the distribution of overt reflexives, which has a functional basis and therefore poses the interesting question whether or not this functional basis is accessible to language learners.

The first part of this commentary discusses the minimal requirements that any serious theory of language acquisition must meet. It must take into account the particular properties of the human language processor and the (linguistic and nonlinguistic) input, as well as the specific motivation which causes the learner to apply the former to the latter. Neglecting, or even not keeping constant, some of these factors leads to a very distorted picture of the nature of language acquisition. In particular, claims about the difference between first (L1) and second language (L2) acquisition that ignore major variation in one of these components go astray.