This paper reviews the biological origins of the critical period hypothesis and the neurophysiological evidence which was initially supplied in support of a critical period for the acquisition of language. Noting the inconclusive nature of neurophysiological evidence, the author suggests that we look to the interplay of affective and cognitive factors in discussing the acquisition of a second language. The main focus of this paper is the consideration of Piagetian cognitive developmental theory in general, and the development of the symbolic function in particular as it relates to the problem of second language acquisition. The suggestion is offered that the onset of Formal Operations may well mark the beginning of the end of a critical period for the acquisition of language. (Author)