 And the last of his writings published in his lifetime (“An Ontological Idealism”) starts with the confession, explicitly employing the same terminology that we have used here: “Ontologically I am an Idealist, since I believe that all that exists is spiritual” (1924 [1934: 273]). He takes spirit to be the sum total of individual spirits or selves connected by the relation of love and bases this conviction on the claim that only this conception of what ultimate reality consists in allows us to overcome unavoidable contradictions connected with all other attempts to reconcile unity and diversity as the distinguishing marks of reality. Harmony between unity and diversity can be established only on the basis of an all-encompassing relation of love between all the characteristic elements of reality, which in turn presupposes thinking of ultimate reality as a community of spirits or as Spirit. These—as McTaggart himself admits (1924 [1934: 271 f.])—rather mystical-sounding assertions, which he adhered to all his life, he tries to back up by a number of different considerations. In his earliest writing he relies heavily on views held by Bradley to the effect that we have to accept that contradictions are a criterion for non-reality. However, he does not employ this criterion as a logical maxim but transforms it into an ontological principle according to which everything that prevents harmony cannot be real. In his last work, his attempt to present an argument for his ontological idealism is based mainly on (1) mereological considerations concerning the structure of substances which aim to show that only spirits can claim the status of a substance, and on (2) his theory of time, the unreality of which he famously had proven in his magnum opus The Nature of Existence (1921/27). In the first volume of this work he attempts to prove by a priori reasoning (NE §43) that all that really exists are substances. Substances according to McTaggart are infinitely divisible and therefore cannot have simple parts. Between substances and their individual features there obtains a relation of determining correspondence such that each feature determines and is determined by all the other. Given these a priori characteristics of what can exist the task McTaggart tackles in the second volume is to 