Answer:
(1) A reverent revival of Classical Greek/Roman art forms and styles; (2) A faith in the nobility of Man (Humanism); (3) The mastery of illusionistic painting techniques, maximizing 'depth' in a picture, including: linear perspective, foreshortening and, later, quadratura; and (4) The naturalistic realism of its faces and figures, enhanced by oil painting techniques like sfumato.
