Psychiatric diagnoses are sometimes made on the basis of criteria concerning the unreasonableness of one’s preoccupations, the unjustified status of one’s doubts, or the disproportionateness of one’s emotional responses. Whereas a bodily diagnosis merely provides one with information, the receipt of these psychiatric diagnoses requires a subtler change of mind. The case of Autism spectrum disorder illustrates one of the ways in which decisions as to the boundaries of psychiatric diagnoses can have consequences outside of the psychiatrist’s therapeutic practice. To take the periodic table as a model for psychiatric diagnoses would be to suppose that the current position with regard to the mental disorders is similar to John Locke’s position with regard to gold and the other elements. If the project of psychiatric classification could be completed successfully, it would bring all of the benefits that usually come with having an established taxonomic scheme.