This chapter provides a brief review of some of the main characteristics of formal aspects of Patty's English idiolect that have emerged from the data. It then turns to a consideration of some factors that have been hypothesized to play a crucial role in adult second language acquisition: native language influence and the possibility of decreased sensitivity to the input. The data suggest that the predictions of the Representational Deficit Hypothesis are not upheld with respect to the L2 acquisition of English past-tense marking by native Chinese speakers. A collection of articles has argued that L1 constraints on prosodic structure play a central role in explaining missing inflection in L2 spoken production. The relevant data that gave rise to B. D. Schwartz and R. A. Sprouse's suggestion about fossilization came from a longitudinal case study of Cevdet, an adult native Turkish speaker acquiring German. The chapter concludes to some extent on one's theory of parameters and their role in learnability.