Linking recent advances in theoretical syntax and empirical research in language development, the book claims that second language acquisition is not totally distinct from first language acquisition, but rather is a replay, a relearning of language. It argues that Universal Grammar is a template guiding acquisition of L1 while constraining acquisition of L2. Assuming that a syntactic distinction crucial for language and its acquisition is the division between lexical and functional categories, it argues that the key to L2 as well as L1 acquisition of syntax is the mastery of morphological features and their linking to functional categories. It thus supports the availability of UG to the second language learner and the minimalist claim that cross-linguistic variation is morpholexical. Constructionism, the hypothesis of L2A proposed in this account, argues for a period of feature underspecification after loss of the L1 value, followed by a progressive building of the L2 value through specific constructions.

We provide a snapshot of childhood morphology development in our investigation of two profiles of bilinguals (age 9–10) in an English-Spanish dual immersion academic setting: Spanish heritage language (SHL,n = 21) and second language (SL2,n = 41) children. Three tasks were given to the 62 bilinguals and 15 age-matched controls (Spanish first language, SL1): oral comprehension of 20 singular-plural present verbs, written sentence production of 10 similar verbs, and a meaning-focused writing task. SHL children were comparable to controls in production of number agreement, and showed no asymmetry between comprehension and production. SL2 learners showed lower accuracy than both SHL and SL1 children. A similar pattern was observed when person agreement and tense, aspect, mood and vowel errors were considered. The most common error among SHL and SL2 children was overregularization of stem vowels, a typical developmental error. The Feature Reassembly model of grammar can accommodate the range of possibilities represented by the data we present.

This article reexamines Bley-Vroman’s original (1990) and evolved (this issue) fundamental difference hypothesis that argues that differences in path and endstate of first language acquisition and adult foreign language learning result from differences in the acquisition procedure (i.e., language faculty and cognitive strategies, respectively). The evolved assessment of the theoretical and empirical developments of the past 20 years is taken into account with respect to Universal Grammar and parameters in generative theory and with respect to cognition and acquisition in data processing. This article supports the spirit of Bley-Vroman’s proposals in light of the discussion of three topics: pathway of acquisition, endstate age of acquisition effects, and language processing by monolinguals and bilinguals. I argue that the difference between child and adult language acquisition is, above all, quantitative not qualitative, a gradient continuum rather than a precipitous break.