The challenge was originally put nearly twenty years ago in the concluding sentences of my initial contribution to a discussion in the now defunct journal University; a contribution reprinted in 1955 in New Essays in Philosophical Theology, and in several other places since then. Those sentences read: ‘We are reassured again. But then perhaps we ask: what is this assurance of God's (appropriately qualified) love worth, what is this apparent guarantee really a guarantee against? Just what would have to happen not merely (morally and wrongly) to tempt but also (logically and rightly) to entitle us to say “God does not love us” or even “God does not exist”? I therefore put to the succeeding symposiasts the simple central questions, “What would have to occur or to have occurred to constitute for you a disproof of the love of, or of the existence of, God?”’