Issues concerning UG access for L2 acquisition as formulated by Epstein et al. are misleading as well as poorly discussed. UG accessibility can only be fully evaluated with respect to the steady state gram mar reached by the learner. The steady state for LI learners is self evidently the adult grammar in the speech community. For L2 learners, however, the steady state is not obvious. Yet, without its clear characterization, debates concerning stages of L2 acquisition and direct and indirect UG accessibility cannot be resolved.

Much second language acquisition (SLA) research confuses the representational and the developmental problems of language acquisition, assuming that attributes of a property theory will explain the transitions between the stages of a psychogrammar, or that induction will explain the properties of the representational systems which encode language. I argue that Principles and Parameter-setting theory deals only with the representational problem, and that induction must play a role in explaining the developmental problem. The conclusion is that both Epstein et al. and the papers they criticize are right; they are just not right about the same issues.

We argue that the model developed in Epstein et al.'s target article does not explain differences between child first language (LI) acquisition and adult second language (L2) acquisition. We therefore sketch an alternative view, originally developed in Clahsen and Muysken (1989), in the light of new empirical findings and theoretical developments.

I examine the target articles hypothesis in light of pidginization and creolization (P/C) phenomena. L1-to-L2 transfer has been argued to be the “central process” in P/C via relexification. This seems incompatible with the view that UC sans Li plays the central role in L2A. I sketch a proposal that reconciles the hypothesis in the target article with, inter alia, the effects of transfer in P/C.

In this commentary, I examine the experiment reported by Epstein et al. in section 5. What I show here is that the experiment is so poorly executed that little, if anything, can be concluded from it regarding the role of UG in L2 acquisition.

The current conception of the relation between UG and the grammar of a language rules out the no-access hypothesis, but does not distinguish between the full-access and partial-access hypotheses. The former raises the issue of why language acquisition in child and adult should be so different. The evidence presented in Epstein et al.'s target article seems inconclusive regarding a choice between hypotheses.

Epstein, Flynn, and Martohardjono trivialize the question of access to universal grammar in second language acquisition by arguing against a straw-man version of the no-access position and by begging the question of how second language (L2) knowledge is represented in the mind/brain of an adult L2 learner. They compound their errors by employing a research methodology that fails to provide any relevant evidence.

The evidence that L2 learners have full access to UG is not convincing. The following will be shown: (1) The argument that L2 learners “expect” L2 to have particular properties rests on the conceptual confusion of having the concept of language (in the sense of knowing the meaning of “language”) with having access to UG. (2) The claim that L2 acquisition takes place under the constraints imposed by universal principles lacks empirical support. (3) The assumption that L2 learners assign new parameter values is based on a problematic example and remains unclear.

The contribution to L2-acquisition which comes from UG is conceptually distinct from that which comes from L1 (or from L1 and L2 jointly), but it is difficult to tease the two apart. The workings of deep, core principles (e.g., locality and subjacency) are so massively evident in L1 and L2 as to be of questionable use in the search for the contribution which is purely of UG.

The implications of Epstein et al.'s critical evaluation of much of the existing literature on L2-acquisition extends far beyond the domain they discuss. I argue that similar methodological clarification is urgently needed in analyses of the role of UG in L1-acquisition, as well as in discussions in such seemingly “distant” areas as the study of language change.

The confirmatory nature of the empirical evidence used to establish UG effects in L2 development is considered. Specific issues are also raised concerning the internal validity of Epstein et al.'s findings. It is concluded that the role of UG in adult L2 development will only be established when researchers better understand the interaction between the development of UG-constrained structural knowledge and the development of overall L2 proficiency.

This commentary focuses on whether the full set of categories is available to beginning L2 learners. After critiquing Epstein et al.'s experimental evidence for the presence of functional categories, I outline the results of an experiment involving English speakers learning Japanese as a second language that does indeed point toward the early presence of fuuctional categories.

Children in a given linguistic environment all uniformly acquire their target language, but adult learners of L2 do not. UG accounts for children's uniform linguistic behavior, but it cannot serve a similar role in accounting for adult learners' linguistic behavior. I argue that Epstein etal.'s study does not answer the question of why L2 learners end up with nonuniform and imperfect linguistic competence in learning a second language.

L2 learners may access UG principles because these are realized in all natural languages. Since this is not the case for the parametrized aspects of language, parameter setting may be progressively replaced by restructuring mechanisms which are specifically related to the process of representational redescription because L2 learners are not sensitive to the [±] features which define parameters.

Epstein et al. take as given that, (1) a hypothetical Universal Grammar (UG) exists that allows children effortlessly to acquire their first language; they then argue (2) that critical or sensitive periods do not block the UG from second language acquisition. Therefore, why can't we all effortlessly “acquire” Tibetan in six months or so? Data concerning the neural bases of language are also noted.

Epstein et al. attribute second language learning to the forces of transfer and language universals. They show that transfer is minimally involved in certain types of learning and therefore conclude that universals are involved. However, they forget to consider the important role of learning in second language acquisition.

If Epstein et al. are right that adult second language learners have full access to UG, then all of the following should be true: adults should be able to consciously transform their I-Language; adults should be able to transform pidgins into Creoles; adults should be as likely as children to restructure their grammars on the basis of “functional” pressure. All the foregoing are false, however, which seriously calls into question the correctness of their hypothesis.

Epstein et al.'s theory of SLA is heavily dependent on assumptions about both the nature of the acquisition device and the grammar that it produces. This commentary briefly explores the consequences of an alternative set of assumptions, focusing on the possibility that the acquisition device does not include UG and that syntactic representations do not contain functional projections.

The range of hypotheses considered is surprising in that the most arguably plausible one is not included: the invariant principles of language are available for life, while the parameters of variation cannot be set after puberty. This hypothesis provides a better explanation than the author's for both the deep similarities and the vast differences between child “language growth” and adult language acquisition.

Curiously, two central areas are unaddressed by Epstein et al.: (i) L1A–L2A differences; (ii) L2 development. Here, findings relevant to (i) and (ii) – as well as their significance – are discussed. Together these form the basis for contesting Epstein et al.'s “Full Access” approach, but nonetheless analyses of the L2 data argue for UG-constrained L2A. Also discussed is the inadequacy of accounts (like Epstein et al.'s) without an explicit and prominent role for the L1.