“There are no objective values.” Not one to waste opening lines, that’s the startling first sentence of J L Mackie’s Ethics: Inventing Right and Wrong. (He didn’t mince words in subtitles either.) An Oxford philosopher, born in Australia 100 years ago this month, his thoughts about metaphysics, logic, and causation still get a hearing in classrooms and conference halls. But what really grabs those inside and outside the ivory tower are his arguments for atheism and scepticism about ethics. His work, worth returning to as the anniversary approaches, is filled with arguments and counter-arguments, so brace yourself for a few premises and conclusions.

In The Miracle of Theism, published posthumously in 1983, Mackie argued that “the question whether there is or is not a god can and should be discussed rationally and reasonably… it can yield definite results.” The results, for Mackie, make a case for atheism. His target was not some ill-defined New Age divinity, but the all-knowing, powerful, perfectly good, omnipresent, eternal creator at the centre of Judaism, Christianity and Islam. Despite centuries of trying, Mackie argues, philosophers and theologians haven’t managed a persuasive proof of the existence of God.

With characteristic rigour he worked through the best of the debate. He looked at David Hume’s treatment of miracles. If you think a miracle is evidence of God’s existence, bear in mind that a miracle is a violation of the laws of nature, and so the evidence we have against miracles is the overwhelming weight of evidence for laws of nature themselves. Mackie considered various takes on the claim that reflection on the idea of God leads to proof that God must exist. You might argue that if God is defined as the greatest conceivable being, and if it’s greater to exist in reality than just in thought, then God must exist.

“‘There are no objective values,’ Mackie wrote. He was not one to waste opening lines”

Called the “ontological argument,” this line of thinking has convinced many. But by this reasoning, we can define all sorts of ridiculous things into existence—how about the Greatest Conceivable Island? Where’s that?

He considered proofs characterising God as the uncaused first cause or as the necessary presupposition of morality, and found them wanting. He also looked at the old idea that the design witnessed in all creation is a sure sign of a designer—but by the same logic, doesn’t…

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