The production of speech is a complex cognitive activity, whose elaboration may be disturbed in various ways. Our purpose here is to explore the continuum between normal and pathological speech production. There are similitudes between performance errors by average speakers and the paraphasias produced by aphasics in the same circumstances; both kinds of perturbations affect the same linguistic units and reveal similar psycholinguistic mechanisms. Yet, production in these two cases differ according to several criteria, such as the error rate, the way the erroneous item and the target item are connected, the speaker's awareness of inadequacy, the comments he makes and his need for justification. Those elements point out to the boundaries that may be defined between normal and pathological speech.

Based on the description of defective verbal forms in stories, we propose an analysis of errors with a didactic aim. The past perfect is a verbal tense that children know well and use spontaneously. Deficient usage in school stories, however, reveals some difficulties when they imagine mentally the succession of the events of a story in the act of writing. Our hypothesis is two-fold : on the one hand the child has difficulties in representing the order of events, on the other he/she has to choose an event which serves as a temporal mark in the story and allows for the use of a past perfect. The study of discourse where the unsuitable form appears, indicates a conflict in the act of writing, i.e. the difficulty of the writer to unify the narrator's point of view.

Based on recent studies that put into question the concepts of prototype and typicality, this study treats the processes of categorization by sufferers from Alzheimer's disease, in the light of two themes: clotting of the prototype into stereotype and distinction between, on the one hand, the representations of common objects developed by an individual in a very early stage of his development and, on the other hand, the socialized attainments acquired subsequently. We analyse the processes of categorization in five groups of subjects (English-speaking students, French-speaking students, sufferers from Alzheimer's disease and witnesses) paired by age, sex and level of studies. Our aim is to study two effects on the probability of categorical inclusion: the effect of constraints and categories (putting in contrast four types of categories - two "natural" ones and two "artefactual" or cultural ones), and the effect of typicality of examples, in the different groups of subjects. By this analysis, we aim to demonstrate specific behaviours shown by the group of sufferers.

Following an empirical study, this article deals with a specific type of errors in vocabulary acquisition of French as a second language: intralingual lexical confusion. 480 English and Greek speaking learners (beginners, intermediates and advanced) of French were given a L2-L1 translation task of French words. A large number of errors revealed confusions due to formal and/or semantic similarity between the target words and other French words known by the learners. The formal and/or semantic comparison between error and target word allowed a narrower description of intralingual lexical confusion highlighting some precise sub-categories of what the author calls "lexical confusibles".