Syntactic Bootstrapping in the Acquisition of Attitude Verbs

Attitude verbs, like think, want and hope, seem to be acquired later than other verbs. Moreover, some attitude verbs (want) seem to be acquired later than others (think). Why should this be? Perhaps observability is a bigger problem than in other cases of word-learning. Psychological events like thinking and wanting do not have direct physical correlates unlike objects like dog or cat, or events like running or eating. Although on the surface, this seems to be a huge problem, it may not be as difficult as it initially appears to be. Advances in cognitive development have revealed that from a very young age, all humans share common conceptual and perceptual capacities, which have been argued to weaken the force of Quine’s famous induction problem. From just a few months old, infants have rich concepts of continuity of objects, gravity, event representation and more (Carey 2009, Eimas & Miller 1990, Soja, Carey & Spelke 1991, Spleke & Kestenbaum 1986, and others), and these concepts shape their perception and attention in a way that may restrict candidate word meanings. In addition, infants have been shown to track the minds of others with astonishing ease. From the first months of life, infants give privileged status to human agents, and are sensitive to conversation partners’ goals and perspectives. They attribute goal-directedness to human agents from as young as 5 months of age (Woodward 1996). This sensitivity to other people’s minds also aids children in language acquisition. Children can track eyegaze and use it to learn new words by 16 months old (Baldwin 1991, Bloom 2000, Plunkett 1997). By age 2, children are adult-like in their interpretation of indexical pronouns, which shift reference based on conversational roles (Moyer, Harrigan, Hacquard & Lidz 2014). Given the salience of psychological states in infant reasoning, linking psychological concepts with words may be no more difficult than linking object and event concepts with words, despite the lack of physical evidence in the world. If, due to this richness of the learners’ representations of other minds, this linking is indeed straightforward, then there is no conceptual barrier to learning attitude verbs. Indeed, some attitude verbs do seem to be acquired easily. Children start producing want to express desires as young as 18 months (Bartsch & Wellman 1995). They further seem to be very good at understanding sentences with want by around 3 years of age (Bartsch & Wellman 1995; Harrigan, Hacquard & Lidz, submitted; Repacholi & Gopnik 1997; Wellman & Banerjee 1991; Wellman & Bartsch 1988; Wellman & Wooley 1990, and others). This suggests that the concept of desire is readily available to very young children, that they are proficient from a very young age at tracking others’ minds, and that their sophisticated cognitive capacities allow them to link the word want to the concept of desire with relative ease. For the verb think, however, we see a different trajectory. Many studies have found that children have difficulty understanding sentences with think well into their fourth year, in particular when the sentences refer to someone’s false belief (de Villiers 2005; 2007; de Villiers & de Villiers 2000; de Villiers & Pyers 2002; Johnson & Maratsos 1977; Lewis 2013; Perner et al. 2003;