 McTaggart endorsed both ontological idealism and epistemological realism. Epistemological realism, as loosely formulated by McTaggart, is the view that knowledge is true (justified) belief, and that truth consists in correspondence with  reality.[15] Ontological idealism is the view that the sum total of all that exists consists in  persons.[16] According to McTaggart, although reality is composed of persons, it does not follow that nothing is real unless it can be known by some  person.[17]