Through exploring CP effects on L2 acquisition we have gained the understanding that age can act in concert with native language influence in manufacturing incomplete attainment in adult L2 acquisition (cf. Birdsong, 1999; Harley & Wang, 1997; Odlin, 1989). Birdsong (1999: 17) points out that 'the CP driven loss of ability and L1 interference are so intertwined that they are hard to separate in the context of SLA, due to the coincidence of the two milestones,' and suggests that the two be traced as jointly underlying adult learners' lack of ability to learn a new language.

L2 research over the last several decades has made available considerable evidence showing L1 as a strong competing causal factor of age-related differences in L2 ultimate attainment. To mention but one recent study, Flege et al. (1995), in their investigation of child–adult differences in L2 phonological acquisition, found that the pre-existent phonetic categories in the adult L2 learners' L1 may restrict their perception of L2 phonetic input. The impact of the L1 on L2 learning appears to be strong and has, in fact, led some researchers to go so far as to claim that 'the price we pay for successful L1 acquisition is the inability to acquire an L2' (Eubank & Gregg, 1999: 92). Given this strong proposition, it would only seem necessary and appropriate that we dwell on the transfer issue in this chapter, in a more complete pursuit of a macroscopic analysis of failure.

A central component of cross-linguistic influence, native language (L1) transfer has been a perennial issue in SLA research. Despite decades of controversies, however, certain generalities that were drawn in the early days of SLA research are still widely accepted today. One such generality was that the L1 constitutes the initial point of L2 acquisition (e.g., Corder, 1967, 1983; Nemser, 1971; Selinker, 1972), and this very same view is still held by many current researchers (e.g.