The acquisition of Dutch modal verbs: necessity versus possibility

A central distinction in the domain of modality is that of modal force, i.e., necessity versus possibility (Kratzer 1991, van der Auwera & Plungian 1998). This distinction is useful to describe the most prototypical meanings of Dutch modal verbs. For example moeten ‘must’ expresses necessity, e.g., obligation, requirement, whereas kunnen ‘can’ expresses possibility, e.g., ability, opportunity, permission. In the acquisition of modality, the role of modal force has not received a lot of attention, as the focus has mostly been on the later acquisition of epistemic modality and on the acquisitional difference in modal source, i.e., participant internal modality before participant external modality (Choi 2006). However, in early Dutch child language, the two most frequent verbs, moeten ‘must’ and kunnen ‘can’, differ exactly in modal force. So, the question arises whether children interpret these modal verbs already adult-like and, more specifically, whether children understand the concepts of necessity and possibility at an early age. In order to investigate this question, 87 Dutch children (age: 3;4 - 6;2) and 18 adult controls participated in a comprehension and a production task. In a truth value judgment task, the children assessed frequent and infrequent interpretations of moeten ‘must’ and kunnen ‘can’. In a story retelling task, they realized frequent and infrequent modal meanings presented through modal verbs, differing in modal force and modal source. The results of the comprehension experiment show that children interpret moeten ‘must’ and kunnen ‘can’ different than the adults. The same is true for the production experiment: children express the target-like modals less often than the adults. These differences in comprehension and production cannot be explained through modal source, but modal force can (partly) account for the differences. In the truth value judgement task, children interpret possibility items less adult-like than necessity items, and in the story retelling task, possibility items are expressed less target-like than necessity items. So, children between the ages of 3;4 and 6;2 struggle with the conceptualization of possibility, compared to necessity. This more adult-like understanding of necessity compared to possibility can be explained through developing cognitive abilities of children, as possibility is cognitively more complex than necessity (Ozturk & Papafragou 2015). Necessity involves a change of the state of affairs, so it has more direct consequences for the child and is hence easier to conceptualize. Possibility requires the understanding of the notion of ‘optionality’, i.e., the existence of several worlds which might not be directly related to the actual world, and are hence more difficult to imagine (O’Neill & Atance 2000). This importance of modal force has already been suggested to explain acquisitional differences in the domain of epistemic modality, i.e., why certainty is acquired before uncertainty (Moore, Pure & Furrow 1990, Ozturk & Papafragou 2015). However, the role of modal force – in contrast to modal source – in the acquisition of non-epistemic modality has not been established before.