Morpheme structure constraints (MSCs or, equivalently, morphemic constraints), i.e., constraints on underived items, pose a logical problem to any theory claiming that the first input list to the lexicon, i.e., the dictionary (DICT), may contain material which is considered ill-formed by the MSCs of the language. This problem is related to Scobbie’s (1991:1) “interaction problem”, i.e., the need to make explicit the way in which constraints, rules and representations interact. In the case of MSCs, the interaction problem can be stated as follows: how can ill-formed material be present in the DICT if the DICT contains constraints, i.e., MSCs, against ill-formed material? The Theory of Constraints and Repair Strategies (TCRS) proposed by Paradis (1988a, 1988b, 1990, 1993, this volume), along with Optimality Theory (e.g., Itô and Mester, this volume, and McCarthy, this volume) but in contrast with Declarative Phonology (e.g., Scobbie, this volume), claims explicitly that the DICT can contain material which is identified as ill-formed by post-morphemic constraints (see Paradis and Prunet 1989a:331; Bagemihl 1991:641; Paradis and El Fenne 1991, 1992, 1993; and Ulrich 1991 for other instances of underlying ill-formedness). To solve this interaction problem, Paradis (1993, this volume) suggests that phonological constraints are active in the lexicon (the component where words are morphologically derived) and the post-lexical level alone, not in the DICT. Structures of the DICT may be identified as ill-formed only when going through the lexicon. The theory of phonology which emerges from this position clearly contradicts the commonly-held view that DICT entries are constrained by MSCs.

I argue here for the necessity of negative constraints, specifically the claim in (1). This position contrasts with that taken by Declarative Phonology (Scobbie 1992; this volume) and with the view that positive and negative constraints are equivalent (Itô 1988:32).

Aphasia refers to an impairment of language processing resulting from brain damage. A very common symptom observed in aphasic speech is the presence of phonemic paraphasias, i.e., phonemic errors involving the substitution, addition or syncope of one (or more) segment(s) in a word stimulus. Phonemic paraphasias can be found across multiple tasks (repetition, reading aloud, spontaneous speech, picture naming) that require a subject to produce a word sound. They are not specific to a particular type of aphasia since Broca’s aphasics, Wernicke’s aphasics, conduction aphasics, and mixed aphasics all produce phonemic paraphasias (see Lecours et al 1983).