Heteroclisis is the property of a lexeme whose inflectional paradigm involves two or more distinct inflection classes. Although heteroclisis is widely observable, its implications for grammatical theory remain underexplored, perhaps because its canonical instances have the appearance of sporadic lexical exceptions. But heteroclisis cannot be assumed to lack any role in the definition of a language's morphology, since (i) it is sometimes highly systematic, involving whole classes of lexemes, and (ii) it obeys a universal constraint. These two facts show that heteroclisis is rule-governed. On the assumption that inflectional morphology involves a linkage of content-paradigms with form-paradigms (Stump 2002), heteroclisis can be seen as a kind of mismatch regulated by rules of paradigm linkage. Such rules account for the range of empirical phenomena subsumed by observations (i) and (ii).

This article reconsiders the development and licensing of agreement as a syntactic projection and argues for a productive developmental relation between agreement and the category of focus. The authors suggest that focus projections are initially selected by a variety of functional heads with real semantic content. Over time however such selected focus frequently decays into a simple concord shell, and when this occurs, the lower half of the shell becomes a simple agreement projection parasitically licensed by the higher functional head, which does have a genuine semantic value.

Jaeger, Lockwood, Kemmerer, Van Valin, Murphy, and Khalak 1996 (Language 72.3) reported an experimental study that provided reaction time and PET neuroimaging data said to support Pinker’s (1991) theory of inflectional morphology in which rule-governed forms and exceptions are processed by separate mechanisms. The results were also taken as evidence against connectionist accounts in which a single processing system generates both types of forms. We provide a critical analysis of the study that yields three main conclusions: First, Jaeger et al.’s data do not provide strong evidence that rule-governed forms and exceptions are processed in separate brain regions. Second, there are problems with the design of the study that contaminate critical comparisons between conditions. The results therefore afford alternative interpretations related to experiment-specific factors rather than the regular-irregular distinction. Third, the dissociations between rule-governed forms and exceptions observed in studies such as Jaeger et al.’s can be accommodated by the connectionist theory. We conclude by offering suggestions for future research that would overcome the major limitations of this study and provide more decisive evidence bearing on the issues.

The effect of the finite ion Larmor radius on the dynamics of two counterstreaming weakly collisional plasma flows in a magnetic field of an arch configuration is considered. Hybrid numerical simulations show that in a system whose dimensions are close to the ion Larmor radius, more intense interaction dynamics is observed and the magnetic arch experiences a significant expansion with the formation of a region with an irregular character of magnetic lines, in which magnetic reconnection processes occur. In this case, the generation of a surface wave of the ion-cyclotron range is observed at the boundaries of the arch. An increase in the scale of the system compared with the ion Larmor radius leads to a transition to the ideal magnetohydrodynamic regime, in which the evolution of the arch occurs much more slowly, and the development of instabilities is not observed.