 Edwards' most impressive arguments from divine foreknowledge are based on the impossibility of knowing future contingents and on the necessity of the past. One knows p only if one has evidence for it, and evidence “must be one of…two sorts, either self-evidence or proof.” Propositions about future contingents can't be self-evident, however, because the states of affairs they represent are neither present to the mind nor necessary. But they can't be proved either, for if the state of affairs expressed by the proposition is genuinely contingent, “there is nothing now existent with which the future existence of the contingent event is [necessarily] connected.” Future contingents are thus necessarily unknowable (Freedom of the Will, 1754; Edwards 1957–, vol. 1, 259). Since God's knowledge of the future is comprehensive, it follows that no future event (and so no future human action) is genuinely contingent.