The problem which I propose to consider is not whether the distinctions past, present, future, characterize the form of time in such a way that whatever may be true concerning the reality of one of these characteristics must be equally true of the others, but the more particular question of the kind of existence which belongs to the content of the past, or its constituents as events.

In her 1938 paper ‘Logical and Metaphysical Necessity’, Martha Kneale introduces the necessarya posteriori. I present a critical summary of Kneale's argument that so-called ‘metaphysical propositions’ are necessary but nota priori. I argue that Kneale is well placed to offer a template for reconciling conceivability approaches to modal epistemology with the post-Kripkean trend for taking metaphysical necessities to have their source in mind-independent reality.