Classes and collections: Principles of organization in the learning of hierarchical relations

This study demonstrates that children tend to distort class inclusion relations (e.g., the relation of oaks to trees) into the part-whole structure of collections (e.g., the relations of oaks to a forest). Children aged 6 to 17 were taught novel class inclusion hierarchies, analogous to the relation between oaks, pines, and trees. In one condition, the class inclusion relations were taught by ostensive definition alone, e.g., stating “These are trees” while pointing to trees and, “These are oaks” while pointing to oaks. in the second condition, children were additionally told what would be analogous to “Oaks and pines are two kinds of trees”. With this additional information to constrain their interpretation, even the youngest children correctly interpreted the relation as class inclusion. In contrast, with limited information, children as old as 14 erroneously imposed a collection structure on the inclusion hierarchies. They would deny, for example, that any single tree was a tree (as they should of they thought “tree” meant “forest”), and would pick up several trees despite being asked for a tree. The results indicated that the part-whole structure of collections is simpler to establish and maintain than the structure of inclusion.