Pain might be a powerful diagnostic tool, but it is at the same time an intensely private and subjective experience that represents a formidable problem in the communication between physician and patient. Galen addresses (principally in De locis affectis) the problem of constructing a consistent and univocal terminology for different pain sensations, rejecting the system proposed earlier by Archigenes on the grounds that he relies on metaphorical descriptors which indiscriminately incorporate terms belonging to information generated by all the senses, fails to conform to patient testimony, and refers to ambiguous concepts. Galen sets himself the task of developing a system of proper or literal (kyrios) terms for pain sensations, even despite the apparent ineffability of certain sensations and laymen's imprecise self-analysis and description of their suffering. His pain vocabulary, developed through a combination of consensus between patients and physicians' expert descriptions of their own pain, promises to link terminology univocally to sensation, turning patients' testimony about their subjective experience of pain into universally applicable diagnostic guidance.