["Mind &Language, EarlyView. ", "\nCognitive scientific explanations can take either a mechanistic or design perspective. Some recent philosophical works propose to apply the mechanistic perspective to the influential mental file framework. The design perspective, however, remains underexplored. This paper takes on this task, arguing that mental files have been designed by natural selection to efficiently represent property cluster structures in the environment—such as objects and kinds—to facilitate our learning about them. It also shows that the design perspective can help resolve a previous debate between two specific accounts of mental files.\n"]