The issue of internal consistency has been raised by Kent (1997) and by Bassi &amp; Ghirardi (1999, 2000) on the grounds that the rules for reasoning using histories, summarized in section 5, lead to contradictions: certain assumptions allow one to derive both a proposition and its contradiction. Equivalently, a quantum property can be assigned, on the basis of the same initial data, probabilities of both 0 and 1. These criticisms have been answered in Griffiths &amp; Hartle (1998) and in  Griffiths (2000a, 2000b). In addition there is a general argument for the consistency of the histories approach in Ch. 16 of Griffiths (2002a). The key point, easily overlooked as it has no close analogy in classical physics, is the single framework rule R3 of section 5. In situations that involve quantum properties at a single time the use of a single framework means the use of a particular projective decomposition of the identity and the associated Boolean event algebra. When reasoning is restricted to this algebra the usual rules of propositional logic apply, so an inconsistency at this level would imply the inconsistency of standard logic. If the framework in question consists of a family of histories of a closed system, it cannot be assigned probabilities using the extended Born rule, subsection 4.2, unless the consistency conditions are satisfied. But in those cases where probabilities can be assigned they satisfy the usual rules of probabilistic reasoning, thus ruling out contradictions.