Tomasello, Kruger & Ratner make the very interesting and valid point that the transmission of culture must depend on understanding others' minds. Culture is shared among a people and is passed on to progeny. The sharing of culture implies that the purpose of (and therefore the meaning behind) any given cultural element (behavioral tradition, word, or artifact) is understood. Because meaning or purpose emanates from minds, something about others' minds must be understood in order to truly learn some element of a culture. It thus makes sense that cultural learning should depend on social-cognitive skills. But what exactly is cultural learning?

There are two rival interpretations of the term cultural learning. In the first, one would define a given type of cultural learning by the type of social-cognitive skill it entails. For example, imitative learning would be defined as any learning of a cultural element in which another's goals or intentions are taken into account. This definition of cultural learning, however, would force Tomasello et al.'s argument into a circle: Imitative learning relies on this social-cognitive skill because imitative learning is defined as learning that relies on this social-cognitive skill. Such a circular definition does not do their argument justice.

Tomasello, Kruger & Ratner deserve congratulations for their well-reasoned ideas on the development of cultural learning. Their arguments are generally convincing, perhaps because their distinctions and developmental relations among types of cultural learning and agency mirror concepts of my own.

Tomasello, Kruger & Ratner relate the evolution of social cognition – the understanding of others' minds – to the evolution of culture. Tomasello et al. conceive of the accumulation of culture as the product of cultural learning, a kind of learning dependent upon recognizing others' intentionality. They distinguish three levels of this recognition: of intention (what is x trying to do), of beliefs (what does x think about p), and of beliefs about beliefs (what does x think y thinks about p). They then tie these levels to three discrete forms of cultural learning – imitative, instructed, and collaborative – which children become capable of when they are 9 months, 4 years, and 6 years old respectively, at least in Western culture where relevant data are available.