 In their commentaries on this paper (1978), Dennett, Bennett, and Harman pointed out that further experimentation was required in order to determine whether a creature possesses the concept of belief (which concept is required in order to have thoughts about another’s mental states). In particular, it would need to be shown that the creature possesses the concept of false belief. Wimmer and Perner (1983) devised a test that purported to show just that. The original test was carried out with normally developing human children and taken to show that the capacity to represent false beliefs is present in 4 to 6 year olds, but absent in 3 year  olds.[15]  Two different proposals have been put forward to explain this developmental change. One proposal (see, e.g., Gopnik &amp; Wellman 1992) suggests that the child possesses a naïve psychological theory that it uses to explain and predict the behavior of others and that gets revised by the child over time. The other proposal (see, e.g., Leslie &amp; Roth 1993) suggests a native, domain-specific (or modular) mechanism that matures at a certain point as what explains the child’s success with the false-belief test.