Idealism is a philosophical theory that holds that reality is essentially mental or spiritual. According to idealism, ideas or mind are the only true reality, while the material world is characterized by change and uncertainty. Idealists believe we should be primarily concerned with searching for eternal truths, as truth cannot be found in the imperfect material world. Some key aspects of idealism include that ideas alone are truly real, the mind is more important than the body, and concepts like chairs would still exist even if all physical chairs were destroyed. Prominent idealist philosophers include Plato, Descartes, Berkeley, and Hegel.