Abstract

This paper argues that three plausible principles are mutually inconsistent: One ought to assert only what one knows; If it is proper to assert some proposition q, then it is, barring special and not very common circumstances, proper to assert any proposition p from which q has been competently inferred; and Some propositions are both properly assertible and known by competent inference from propositions which one does not know. Each pair of two principles constitutes an argument against the remaining principle, but which principle should one drop?