In Doing without Concepts, Machery (Reference Machery2009) provides a solid argument for how the current construct of “concept” has led to useless controversies. While agreeing that research on concepts needs to be refocused, we contend that Machery's proposal is only a small step towards a new framework for thinking about concepts. We suggest that a promising direction for concepts exists in research that is too often ignored – the acquisition, formation, and development of concepts.

Unfortunately, like many theories in cognitive science and philosophy, Machery's proposal largely ignores development. Doing without Concepts avoids issues that are central to a theory of concepts: how concepts are acquired, how conceptual structures change across development, and how concepts that are coordinated early in development become uncoordinated over time. In fact, Machery's proposal acknowledges the sentiment that development is less important than other areas of research on concepts (2009, p. 18). This blanket rejection of development is erroneous and dangerous – identifying the mechanisms by which concepts are acquired, how knowledge changes over time, and how cognitive processes give rise to such changes is essential to our understanding of how concepts operate and are organized. Because of the focus on such issues, many developmental researchers have taken a step back from the assumption that concepts originate from existing mental structures or representations.

One way that developmental research has advanced our understanding of concepts is by introducing the idea that concepts are formed in the moment (e.g., Gibson Reference Gibson1969; Samuelson et al. Reference Samuelson, Schutte and Horst2009; Smith et al. Reference Smith, Thelen, Titzer and McLin1999; Spencer & Schöner Reference Spencer and Schöner2003; Thelen & Smith Reference Thelen and Smith1994). By this account, performance on tasks is a reflection of the dynamic interaction between the learner and the learning environment – prior experiences recalled from long-term memory act together with task dynamics, perception, and action, to generate behavior. For example, one study (Samuelson et al. Reference Samuelson, Schutte and Horst2009) had children generalize novel nouns for rigid and deformable objects in two different tasks: a forced-choice task, in which children had to choose one of three objects that shared the same name with an exemplar, and a yes/no task, in which children had to respond whether each of the three objects shared the same name with an exemplar. Children's performance in the two tasks suggested conflicting conclusions about how children organized categories. Performance on the forced-choice task suggested that children treat rigid and deformable things differently when assigning labels: Rigid things are named by similarity in shape, whereas deformable things are named by similarity in material substance. However, performance on the yes/no task suggested that children did not distinguish between rigid and deformable things in naming and generalized names for both kinds by shape similarity. Given that children were all at the same developmental level and were presented with the exact same stimuli, differences in performance between the two tasks were likely not attributable to possessing different object concepts. Instead, children's object concepts were formed in the moment given the demands of the different tasks.

Machery notes that the feasibility of concepts being formed in the moment fails because there is not a significant body of research suggesting a “variability across contexts of the knowledge brought to bear on tasks” (2009, p. 22). However, Machery ignores countless examples of developmental research demonstrating great variability in the knowledge that is brought to bear in a particular task (e.g., Plumert Reference Plumert and Kail2008; Samuelson et al. Reference Samuelson, Schutte and Horst2009; Sandhofer & Doumas Reference Sandhofer and Doumas2008; Siegler Reference Siegler1994; Smith et al. Reference Smith, Thelen, Titzer and McLin1999; Thelen & Smith Reference Thelen and Smith1994; van Geert & van Dijk Reference van Geert and van Dijk2002; Vlach et al. Reference Vlach, Sandhofer and Kornell2008). This literature has demonstrated that performance on tasks is flexible (e.g., Sloutsky & Fisher Reference Sloutsky and Fisher2008), context dependent (e.g., Samuelson & Smith Reference Samuelson and Smith1998), and altered by seemingly minor changes in the conditions of the task (e.g., Sandhofer & Doumas Reference Sandhofer and Doumas2008; Sandhofer & Thom Reference Sandhofer and Thom2006; Vlach et al. Reference Vlach, Sandhofer and Kornell2008). For example, altering the timing of exemplar presentation by a matter of seconds can lead to marked differences in children's performance on a generalization task (e.g., Vlach et al. Reference Vlach, Sandhofer and Kornell2008).

Machery also rejects the idea that concepts are formed in the moment, too quickly dismissing the proposal that there are not enduring mental structures for prototypes, exemplars, and theories. The book refers to this perspective as the “anti-representationalist argument” (2009, p. 222). However, developmental research has provided substantial evidence suggesting that variability and behavior can be explained without the presence of a mental structure or representation (e.g., Samuelson et al. Reference Samuelson, Schutte and Horst2009; Smith et al. Reference Smith, Thelen, Titzer and McLin1999; Spencer & Schöner Reference Spencer and Schöner2003; Thelen & Smith Reference Thelen and Smith1994). For example, Piaget (Reference Piaget1954) originally attributed errors in the A-not-B task to infants' lack of an “object concept” (i.e., an enduring mental structure about the spatial and temporal consistencies of objects). Over the last few decades, research has demonstrated that errors on this task result from factors other than a lack of an object concept (e.g., Smith et al. Reference Smith, Thelen, Titzer and McLin1999), such as visual input (e.g., Butterworth et al. Reference Butterworth, Jarrett and Hicks1982), direction of gaze (e.g., Horobin & Acredolo Reference Horobin and Acredolo1986), and memory (e.g., Diamond Reference Diamond1985). Moreover, performance on this task can be explained by the interaction of these processes alone (e.g., Smith et al. Reference Smith, Thelen, Titzer and McLin1999). Altogether, this work has provided a compelling argument for how concepts and performance are shaped in the moment from a confluence of factors, rather than being accessed from an enduring mental structure.

To conclude, thinking about concepts needs a better direction. However, any theory of concepts would be remiss if it did not account for development. We propose that thinking about concepts should be situated within a dynamic framework that includes the learner and learning environment. Future research should explore the mechanisms by which concepts emerge in the moment – perception, action, and memory, interacting with properties of the environment, will reveal how this process works. This framework accounts for how concepts arise and change over time and thus holds great promise as the new direction for thinking about concepts.