However, more than being simply the subject of art, models are often thought of as muses , a source of inspiration without whom the art would not exist. Art models are often paid professionals with skill and experience but are rarely employed full-time, and artists may also rely on friends and family to pose. Paid art models are usually anonymous and unacknowledged subjects of the work. Models are most frequently employed for art classes or by informal groups of artists that gather to share the expense of a model. Models are also employed privately by professional artists.