Heyes argues that nonhuman primates are unable to imitate, recognize themselves in mirrors, and take another's perspective, and that none of these capabilities are evidence for theory of mind. First, her evaluation of the evidence, especially for imitation and mirror self-recognition, is inaccurate. Second, she neglects to address the important developmental evidence that these capabilities are necessary precursors in the development of theory of mind.

The question, “Does the chimpanzee have a theory of mind?” is logically identical to the question, “Does the chimpanzee have a soul?” It is a peculiarity of our culture that we talk about anyone having a mind, and such talk is unhelpful for a science of behavior. The label “killjoy hypothesis” is an ad hominem attack.

Rather than dealing with the important issues in the interpretation of behavioural data, Heyes seems only to reiterate lessons well-learned before she first reviewed the topic of primate deception. She also appears to misrepresent a series of published analyses. Despite her emphatic denials, the commonsense view is the best: informed observations and experiments can both provide evidence of theory of mind.

Heyes's proposed study for testing whether chimpanzees have a theory of mind is (1) too strong because it requires that the animals apply mental concepts to the interpretation of both their own experiences and the behaviours of others, and (2) too weak because dispositional rather than representational understanding of “seeing” is sufficient to pass it.

Heyes's attempt to reinterpret research on primate cognition from the standpoint of radical behaviorism is strong on dialogue and debate but weak on evidence. Recent evidence concerning self-recognition, for example, shows that her arguments about differential recovery from anesthetization and species differences in face touching as alternative accounts of the behavior of primates in the presence of mirrors) are invalid.

Heyes's claim that the only unequivocal evidence of motor imitation comes from rats and budgerigars is contested. It is suggested that the rats' behavior can be explained by emulation and the budgerigars' by response facilitation. Behavioral matching in chimpanzees (Custance et al. 1995; Whiten et al. 1996) is reconsidered and interpreted in terms of imitation.

This commentary criticizes nonverbal methods of assessing theory-of-mind on the basis of prior training of the critical response because they would encourage simple, nonmentalistic, associative solutions even in subjects with mentalistic capacities. I propose instead a new experimental paradigm based upon the use of spontaneous responses in less artificial situations. This method has already provided positive evidence of some level of ToM understanding in nonhuman primates.

Two substantive comments are made. The first is methodological, and concerns Heyes's proposals for a critical test for theory of mind. The second is theoretical, and concerns the appropriateness of asking questions about theory of mind in nonhuman primates. Although Heyes warns against the apparent simplicity of the theory of mind hypothesis, she underplays the linguistic implications.

Given Heyes's construal of “theory of mind,” there is still no convincing evidence of theory of mind in human primates, much less nonhuman. Rather than making unfounded assumptions about what underlies human social competence, one should ask what mechanisms other primates have and then inquire whether more sophisticated elaborations of those might not account for much of human competence.

We suggest that anecdotes have evidentiary value in interpreting nonhuman primate behavior. We also believe that any outcome from the experiments proposed by Heyes can be interpreted as a product of previous experience with trainers or as associative learning using the experimental cues. No potential outcome is clearcut evidence for or against the theory of mind proposition.

Three- to six-year-olds were given Heyes's proposed task and theory of mind tasks. Although they correlated, Heyes's was harder; only 50% of participants with a theory of mind reached a criterion of 75% correct. Because of the complex series of inferences involved in Heyes's task, it is possible that one could have a theory of mind and fail Heyes's version.

That organisms have a concept “see” does not necessarily entail that they attribute knowledge to others or predict others' behaviors on the basis of inferred mental states. An alternative experimental protocol is proposed in which accurate prediction of the location of an experimenters' impending appearance is contingent upon subjects' attribution of knowledge to the experimenter.

We propose a naturalistic version of the “guesser–knower” paradigm in which the experimental subject has an opportunity to choose which individual to follow to a hidden food source. This design allows nonhumans to display the attribution of knowledge to another conspecific, rather than a human, in a naturalistic context (finding food), and it is readily adapted to different species.

Heyes correctly points out some problems in primate theory of mind, but lacks a critical approach to children's theory of mind, and at times implies meta-awareness when discussing theory of mind. Also, in selecting pure experimental designs, she ignores its limitations, as well as the merits, and at times the necessity, of other methodologies.

Heyes's literature review of deception, imitation, and self-recognition is inadequate, misleading, and erroneous. The anaesthetic artifact hypothesis of self-recognition is unsupported by the data she herself examines. Her proposed experiment is tantalizing, indicating that theory of mind is simply a Turing test.

Study of “theory of mind” in nonhuman primates is hampered both by the lack of rigorous methodology that Heyes stresses and by our lack of knowledge of the cognitive neuroscience of nonhuman primate conceptual structure. Recent advances in this field indicate that progress can be made by first asking simpler research questions.

Heyes argues that we need alternative experiments to study those animal abilities generally considered to involve “theory of mind.” The studies she proposes, however, have as many problems as those that she criticizes. Further interactions should exist among researchers examining these capacities before additional experiments are undertaken.

Progress in the “theory of mind” debate would be better served at this point by abandoning the search for a perfect “critical experiment” and developing an incremental research program based on a systematic theory of “theory of mind.” Studies using the goggle procedure advocated by Heyes should dissociate the ability to see from possible behavioral artifacts of “blind” trainers.

We doubt that theory of mind can be sufficiently demonstrated without reliance on verbal tests. Where language is the major tool of social manipulation, an effective theory of mind must use language as an input. We suspect, therefore, that in this context, prelinguistic human and nonhuman minds are more alike than are human pre- and postlinguistic minds.

Great apes show behavioral evidence for secondary representation similar to that of children of about two years of age. However, there is no convincing evidence for metarepresentation in apes. A good evolutionary interpretation should be parsimonious and must bring developmental and comparative data in accord. I propose a model based on the work of Perner (1991) and close by pointing out a logical flaw in Heyes's second proposed experiment.