Harvey Lederman

The difficult phrase ὅ ποτε ὄν ἐστι (hereafter ‘OPO’), which occurs in key passages in Aristotle’s discussions of blood and of time, has long vexed interpreters of Aristotle. This paper proposes a new interpretation of OPO, which resolves some textual and interpretative problems about Aristotle’s theories of blood and of time. My interpretation will also shed light on more general issues in Aristotle’s metaphysics. In the passages I will discuss, Aristotle takes both blood and time to be examples of his peculiar ‘coupled entities’. He then uses OPO to provide explanations which differ from what we might call his ‘standard’ metaphysical explanations. On the ‘standard’ approach, Aristotle explains derivative entities—non-substances—by describing their relationship to substances. By contrast to this standard form of explanation, when Aristotle uses OPO he explains blood and time by describing their relationship to non-substances. This paper thus identifies a new species of metaphysical dependence in Aristotle. In addition, it provides detailed examination of evidence concerning whether Aristotle himself used coupled entities in his own physical and metaphysical theories

Robert Aumann presents his Agreement Theorem as the key conditional: “if two people have the same priors and their posteriors for an event A are common knowledge, then these posteriors are equal” (Aumann, 1976, p. 1236). This paper focuses on four assumptions which are used in Aumann’s proof but are not explicit in the key conditional: (1) that agents commonly know, of some prior μ, that it is the common prior; (2) that agents commonly know that each of them updates on the prior by conditionalization; (3) that agents commonly know that if an agent knows a proposition, she knows that she knows that proposition (the “K K” principle); (4) that agents commonly know that they each update only on true propositions. It is shown that natural weakenings of any one of these strong assumptions can lead to countermodels to Aumann’s key conditional. Examples are given in which agents who have a common prior and commonly know what probability they each assign to a proposition nevertheless assign that proposition unequal probabilities. To alter Aumann’s famous slogan: people can “agree to disagree”, even if they share a common prior. The epistemological significance of these examples is presented in terms of their role in a defense of the Uniqueness Thesis: If an agent whose total evidence is E is fully rational in taking doxastic attitude D to P, then necessarily, any subject with total evidence E who takes a different attitude to P is less than fully rational.