Sympathy (from the Greek words syn "together" and pathos "feeling" which means "fellow-feeling") is the perception, understanding, and reaction to the distress or need of another human being. This empathic concern is driven by a switch in viewpoint, from a personal perspective to the perspective of another group or individual who is in need. Empathy and sympathy are often used interchangeably. Sympathy is a feeling, but the two terms have distinct origins and meanings. Merriam Webster defines empathy as "the feeling that you understand and share another person's experiences and emotions : the ability to share someone else's feelings." Their definition of sympathy is "the feeling that you care about and are sorry about someone else's trouble, grief, misfortune, etc. : a feeling of support for something : a state in which different people share the same interests, opinions, goals, etc." See professor Paul Bloom on empathy.