Some have argued that because artifacts are not natural kinds, they fall outside of the domain of the theory-theory of concepts. To the contrary, artifact concepts function very much like natural kind concepts. A causal-explanatory structure known as 'the design stance' underlies adult concepts of artifacts. According to the design stance, each artifact's existence, kind, and properties can be explained by the function intended by its designer. The notion of intended function constrains reasoning about artifacts just as representations of causal essences constrain reasoning about natural kinds. Furthermore, just as some framework theories that constrain representations of natural kinds, such as a vitalist biology, must be constructed in childhood, so too the design stance is not constructed until the late preschool years (being consolidated between four and six years of age.) Unlike vitalist biology, though, the construction of the design stance builds upon developmental primitives that are part of the early developing systems of infant core knowledge, especially those within core knowledge of intentional agency.