Introduction: Modals and language–thought issues

The ability to communicate through language is a benchmark of human competence. Speakers use language to communicate their knowledge and beliefs and to share their community's rules of social order and cultural norms. Modal expressions, because they encode the stances speakers take on propositions, are essential to these two language functions. Consider, for example, a proposition like John come. With the addition of a modal, such as can, may, must, or will, speakers can make a variety of statements about that proposition, from expressing their degree of certainty about the likelihood of the event it encodes to giving permission for the event to occur. If children are to become competent members of their language community, it is crucial that they master their language's modal system.

Because modal expressions encode notions of necessity, possibility, obligation, and permission, they are an important and revealing aspect of language to study with regard to language–thought issues. The use of modals in the epistemic sense (having to do with beliefs, attitudes, and knowledge states) seems to entail the ability to assess one's own knowledge state, to evaluate evidence, and to communicate those assessments to another whose state may be different from one's own. Such abilities, central though they are to a host of cognitive activities, have not regularly been accorded to children younger than 4. Yet children younger than 4 certainly produce modals in their spontaneous speech. Possibly children use these words solely for purposes of social regulation and description, that is, with deontic and dynamic meanings rather than epistemic ones (Palmer, 1979).