RADIO / Might is on their side: Robert Hanks considers possibilities and probabilities

YOU CAN picture the scene: somebody sitting around in a BBC canteen muses aloud - 'For all sad words of tongue and pen, the saddest are these: 'It might have been]' ' A bulb clicks on in the brain of some sharp young radio producer: what a great idea for a programme . . . and so What If . . . ? (Radio 4, Tuesday).

A mild problem for What If . . . ?, in which the historian Christopher Andrew asks guests to wonder how things could have turned out, is that the number of possibilities is always infinite; and before Andrew can even start to prune the hypotheses down to manageable proportions, you have to know what happened in the first place - and even in something as recent as, say, Mrs Thatcher's resignation of the premiership (the topic a couple of weeks ago), that can be open to doubts and alternative interpretations. So there's a constant sense that what really happened is uncertain enough to make this sort of conjecture seem frothy and insubstantial.

In what some might see as a natural progression from the Thatcher programme, last week's programme asked the big one: what if Jesus hadn't been crucified? This question is particularly thorny (if that isn't a tasteless adjective in the context), not only because such a vast swathe of history depends on it, but because to discuss it at all you must first admit that the event wasn't pre-ordained - so you've already downgraded the question's supposed importance before you're even started.

For the occasion, a conscientiously ecumenical panel was assembled - a Christian, a Muslim and a Jew (the Rev Tom Wright, Mashuq Ally and Rabbi Julia Neuberger). The respect for one another's faith meant that God mostly got left out of the equation. Only Mashuq Ally was prepared to talk about him directly, suggesting that, had Jesus lived, God wouldn't have had to turn to the Arabs - though later, pressed to speculate, he suggested that, if God was going to choose anybody, the Arabs would probably be it, since the Jews had by this point blown their chance.

The other mild oddity about the panel's make-up was that once it had been established that Christ didn't get crucified, leaving Christianity finding a new marketing symbol to replace the cross, or not coming into being at all, Tom Wright didn't really have anything left to say on his own behalf. All he could do was commentate from time to time and speak up for paganism.

But the valuable thing about this programme, as about all the best editions of What If . . . ?, was the oblique light shed on other issues, particularly in the later stages of the programme, when the inhibitions began to break down. Christopher Andrew laid into Mashuq Ally's vision of a democratic Islamic utopia; Julia Neuberger was cornered into admitting that she thought there might have been no Holocaust without Christianity and its institutionalised intolerance.

You didn't in this case learn a lot about what was or might have been; but it was worth hearing what people thought about what is.

A Look Back at the Nineties (Radio 4, Friday) plays a slightly different game with conditional tenses, forgetting the might-have-beens in favour of the could-still-happens. The idea is that it's New Year's Eve 1999, and Brian Perkins is introducing a retrospective of the decade on BBSkyC; every week we get a different year - this week, 1996.

At first sight, this looks like an extended version of Week Ending's venerable 'Next week's news' slot, and there are occasional bursts of topicality, like the one about Group 4 Security losing their government contract - they were taking it from Whitehall to their office. But the future is here just a convenient peg for the humour. Other jokes could as easily have come out of A Look Back at the Eighties (the Government is selling off the notes of the musical scale - G has been replaced by a voice saying 'Come, to the Moghul Tandoori in Bedford'). In Week 1, it looked rather promising, freewheeling but with enough structure to keep the momentum going. Perkins' news bulletins were a neat device for cutting sketches short. This week's programme blew it, though - jokes with weak premises ('A hedge is for life, not for Christmas') and feeble punchlines. And it all looked so promising: when you think about what might have been . . .