If you have an iphone or an ipad, you will have met Siri, the electronic personal assistant. The geeks in Silicon valley have become more humorous as they have programmed her to answer a wide range of questions.

They have begun to flex their humour muscles. If you ask Siri to help you through the day with a joke or two you may get; “the past, present and future walked into a bar one day. It was tense.”

She even does pathos and sarcasm. If you explore romance with her and ask “Siri, do you have a boyfriend?” One of her answers is “Why? So we can get ice cream together and listen to music and travel across galaxies, only to have it end in slammed doors, heartbreak and loneliness ? Sure where do I sign up?”  For anyone with a broken heart, this is tender territory. But once past a certain point, laughing helps not hurts.

They are playing it fairly safe, because  jokes can present a bit of a risk. But they have a number of functions,

Jokes can be dangerous; jokes can be healthy; and jokes can be therapeutic. While they look at first sight as though they are just about funny, in fact they are to do with power and incongruity as well as joy or fun.

Why are jokes sometimes dangerous? Because they act like banana skins under the shoes of the powerful and pompous. That’s why some of us like them so much. The powerful and pompous are hard to hold to account, but jokes start the process.

One of the most impressive films for placing a banana skin under a dictator’s boot was Charlie Chaplin’s ‘The Great Dictator’ (1940) where he imitates Hitler and parodies him mercilessly.

Chaplin wrote in his autobiography,  “It is paradoxical that tragedy stimulates the spirit of ridicule. Ridicule, I suppose, is an attitude of defiance.” Sometimes the only defiance you can afford to risk is humour.

Quite how dangerous jokes can be in a different context we discovered when the cartoonists and journalists of the Charlie Hebdo magazine which published cartoons about Mohammed and bombs, were assassinated by Muslim activists in Paris. In 2015. Two Muslim brothers walked into the magazine’s offices and shot dead 12 people, and seriously wounded another 11.

It raised the question of what happened when you used jokes to hold religion to account.

It has been interesting to hear how the Monty Python team have reflected recently on how easily they made fun of Christianity and clergy, and in the Life of Brian, coming within a hair’s breadth of making fun of Jesus. But they rightly claimed they were making fun of Christians, especially the pompous ones. There were no consequences for them except bigger box offices. Most Christians laughed with them. They wouldn’t dare treat Islam in the same way.

Boris Johnson stepped into the same arena last week and provoked outrage because he dared to make a joke about the burka. He wrong footed a lot of his would-be critics by making the liberal case against banning it. But too many people couldn’t get beyond the post-box joke. How dare he cause such offence against Muslims by making a joke about what the more extreme followers wear?

It raises the question as to why is there such a difference between Islam and Christianity when confronted by humour? Why didn’t a squad of Christian activists take down the Monty Python team, or the director of ‘The Last Temptation of Christ’?

It seems to have something to do with the fact that Christianity and Islam are radically different as ways of dealing with the mysteries of life.

At their heart the two religions are doing very different things. Our relativistic culture doesn’t manage the difference very well. Christianity has at its heart not power but love. Love laughs more easily when teased than power does.

Islam is a hybrid mixture of religion and politics and is deeply concerned with the exercise of power. After all, Islam means submission.  You have to submit to God and the Koran. It is an exercise in both religious and political control.

The wearing of the burka does seem to be more than a statement about modesty. It is also an exercise in power. The observer sees nothing, and knows nothing about the person hidden in it, and so is disempowered from either any relationship or any kind of assessment.

When we meet power in public life, we can either submit, challenge or laugh. Submission requires too high a price. A challenge risks conflict. Laughter may be preferable to both, and tests the intention and practice of power.

In the wake of Boris Johnson’s letter-box and bank robber quips, and the response which tried to shut the humour down because all criticism was not allowed, because it caused offence, what should we do? Allow power to become more powerful? Or welcome humour to hold it to account when it overreaches itself and becomes ridiculous? As Charlie Chaplin said, “sometimes the only defiance you can afford to risk is humour.”