The term "anhedonia" is derived from the Greek "an-", "without" and "hēdonē", "pleasure". Interest in the nature of pleasure and its absence dates back to ancient Greek philosophers such as Epicurus. The symptoms of anhedonia were introduced to the realm of psychopathology in 1809 by John Haslam, who characterized a patient suffering from schizophrenia as indifferent to "those objects and pursuits which formerly proved sources of delight and instruction". The concept was formally coined by Théodule-Armand Ribot and later used by psychiatrists Paul Eugen Bleuler and Emil Kraepelin to describe a core symptom of schizophrenia. In particular, Rado postulated that schizotypes, or individuals with the schizophrenic phenotype, have two key genetic deficits, one related to the ability to feel pleasure (anhedonia) and one related to proprioception. In 1962 Meehl furthered Rado's theory through the introduction of the concept of schizotaxia, a genetically-driven neural integrative defect thought to give rise to the personality type of schizotypy. Loren and Jean Chapman further distinguished between two types of anhedonia: physical anhedonia, or a deficit in the ability to experience physical pleasure, and social, or a deficit in the ability to experience interpersonal pleasure.