What the mental lexicon might be
The nature of the mental lexicon remains one of the central controversies in cognitive science, bearing on fundamental questions concerning the representation and processing of linguistic knowledge. In this article, we examine Gary Libben’s contributions to the study of lexical representation and processing, with particular focus on the theoretical and empirical studies leading to the “flexicon” framework. We address four interrelated questions that have guided both Libben’s research program and broader debates in psycholinguistics: (a) What are the basic units of lexical representation? (b) Do morphologically complex words undergo decomposition during recognition? (c) To what extent are perceptual analyses constrained by morphological principles? And (d) does semantic information penetrate the earliest stages of lexical processing? Drawing on Libben’s theoretical writings and a selection of empirical studies spanning four decades of research, we situate his proposals within competing accounts of the mental lexicon, including symbolic, connectionist, Bayesian, and hybrid approaches. We argue that the flexicon framework represents an attempt to reconcile aspects of these traditions by combining morphemes and full-word forms, dynamic lexical representations, and usage-based influences within a system aimed at maximizing opportunities for lexical use. We review evidence from studies involving aphasia, deep dyslexia, compound processing, and morphological ambiguity in trimorphemic words, assessing the extent to which the findings support the framework’s central claims. While the flexicon provides an innovative perspective on lexical flexibility and morphological productivity, we argue that several questions remain regarding the role of constituent structure, morphological computation, and semantic information in lexical processing. We conclude by suggesting that the flexicon is best viewed as a research program that raises important questions about the relationship between lexical representations, linguistic structure, and language use.