I promised last week I would offer full argument in this week’s column for why morality does not need God. Now that my public debate with Professor John Lennox has come and gone – I can set out my basic argument for those who were not there.

Although the debate lasted some 90 minutes, the problems with Christian ethics are so incredibly basic that I can confidentially assert I can put Christian ethics on the back foot in under 800 words here.

Is murder wrong because God says so or does God tell you not to murder because it is wrong regardless of what God thinks? How about rape? Is rape wrong only once God sends us a command, ‘Thou shalt not rape’ or is rape wrong whether or not God commands us to not rape?

Christians – and those of other faiths – have a huge problem answering these questions. They have two choices: either they can say rape is wrong because God or Allah or Whoever doesn’t want us to rape or they can say that God reminds us to not rape because rape is wrong as a matter of universal moral truth, that is, independent of God. But watch where that leads you.

If things are right or wrong only once God has given his view, then morality becomes arbitrary. We are at that point at the whim of God. If you’re an obedient Christian, this logically forces you to accept that if a missing page from the bible is found tomorrow that says, ‘Kill all racists on on-line comments sections’, then you must do so. It is God’s command.

Well, Mr and Ms Christian, would you willy-nilly follow commands from God regardless of whether you feel comfortable with them? Would you? Is that a ‘No’ I am hearing from you? Good. Because presumably you will only follow moral commands that are rational and meaningful.

So, we can safely conclude that it is not desirable for morality to be based purely, and uncritically, on God’s wishes. We want more. We want reasons.

There is good news. You could, instead, accept that God tells you not to murder because murder is wrong. Murder is wrong whether or not God exists. And if God says to you you should not murder, he isn’t inventing a fresh, new, moral command; he is simply communicating a moral command that exists widely for good reasons

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So Christians, and other faiths including Islam and Judaism, must make up their minds: Do you follow commands regardless of what they are? Or do you concede you can tell me why cheating or killing or raping or terrorism are all wrong without making references to supernatural beings? And the truth is you know you can articulate the wrongness of these activities without reference to a God. That means God is not needed for morality.

I was shocked that Professor Lennox’s main response to me was that he partly agrees. I asked him if he could write me a 500 word essay, without making reference to his Christian God, but still explaining fully why it is wrong to murder. He said yes. That is a gigantic concession that is going to be archived on YouTube. Yes I am pleased about that. Many Christians would have said ‘No, it is not possible’.

He then explained why it is only a partial concession, he said God plays an important role as God gives him, and me, the rationality that helps us to reason about morality. So while we can reason about the wrongfulness of murder with no reference to God, God is responsible for the rational capacity that enables us to reason.

This is a shockingly poor retort, and one he has trotted out many times in debates with others. So what if he gave me the capacity to reason? It still remains that people can, as Lennox conceded, reason about morality without praying to God, without consulting the bible. That means God is not necessary for us to distinguish between right and wrong.

The conclusion remains: we know rape is wrong without asking God if it is wrong. In the context of reflecting on the connection between morality and God, we can conclude that God plays no epistemic role in the explanation and justification of moral rules that govern our societies.

Lennox’s argument is a bit like saying that just because my mom gave birth to me, she is a necessary part of the explanation of how I solve a maths problem. Without her, I wouldn’t exist. That is true, but it is an utterly uninteresting truth when you congratulate me for winning a Maths Olympiad.

So thanks, God, for giving me rationality. But sorry dude that means you are not needed beyond that.

If you disappeared permanently tomorrow, I’ll still know the difference between right and wrong.