The chapter presents Stampean Natural Phonology’s perspective on L2 phonology development in adult learners, emphasizing that this process is shaped by the same forces that govern L1 acquisition. Central is the concept of phonological processes, that is, phonetically motivated substitutions that arise in response to perceptual or articulatory difficulties. Phonological learning is seen as suppressing processes unsupported by the ambient input. Transfer is a byproduct of the automatic application of unsuppressed processes to L2 representations. Natural processes differ from morphonological rules, which are consciously learned patterns that rarely transfer. Next, the chapter examines speech perception and phonological representations in infant and adult learners, discusses the interplay of fortitions and lenitions, explores how latent L1 processes may surface in L2, and how phonological representations are updated by inhibiting additional processes. The chapter turns then to speech production, exploring the constraints on learning new percept–gesture mappings by adults and considers whether L2 learners can relax the suppression of a natural process previously inhibited in L1.

The Cambridge Handbook of Natural Linguistics aims to provide a comprehensive state-of-the-field survey of the developments in phonological, morphonological, and morphological, as well as syntactic, pragmatic, and textlinguistic theory that have arisen from or are related to the theory of Natural Phonology. This kind of synopsis of the Natural Linguistic paradigm has not been offered yet. The Handbook includes an in-depth account of the origins and foundational principles of the theory of Natural Phonology, followed by extensive delineation of the semiotic, cognitive, and functional bases of Natural Linguistics, as well as interpretations of the term “natural.” Further parts extend beyond phonology and provide overviews of morphology, syntax, phonotactics and morphonotactics, pragmatics, text, and discourse, and dwell on a variety of external evidence for the theory. A critical appraisal of the position of Natural Linguistics among modern linguistic theories concludes the Handbook.

A natural phonological process is a mental substitution that responds in real time to an innate limitation of the human ability for speech perception and production. Processes are responsible for the discrepancies between the perceived and intended (lexical) representations of words and morphemes and the targets for their actuation in speech. They adjust prosodically mapped mental representations, changing some features of an intended utterance. Because these features are associations between articulatory gestures and their auditory effects, hearers can attribute the discrepancies to the application of processes. Processes are universal since they arise in universal articulatory and perceptual abilities. Inhibiting different processes makes phonologies differ from each other. The inhibitions are mastered in acquiring the pronunciation of a language. Processes that remain un-inhibited/active govern allophony, automatic alternations, variation, one’s native accent, and one’s foreign accent in L2. Processes are entirely phonetically conditioned. Phonological processes may be fortitive (to enhance properties of individual segments) or lenitive (to ease production of sequences).