- “Do you not realise that you too could create all these things in a sense?"

- “And what sense is that?” he said.

- “It’s not difficult,” I said. “You could do it anywhere you like and as quickly as you like – quickest, I suppose, if you took a looking-glass and held it up all around you. You could make the sun in an instant, and everything in the sky; the earth in an instant, yourself in an instant, and all the other animals and tools and plants and all the other things we were just talking about.”

- “Oh, sure,” he said, “as they appear – but not as they really are.”

Plato, Republic X 596d-e

The best insults come back as banners. “Tory” originally meant outlaw or rebel – coined from the Irish word for “pursue” – until it became a badge of honour for the Royalist faction in Parliament under Charles II. The “Impressionist” movement took its name from a sneer by the art critic and satirist Louis Leroy, who lambasted Monet’s Impression: soleil levant in an imagined dialogue between two viewers.

Playwrights, too – the ultimate object of Plato’s crashing irony in the first half of Republic Book 10 – have taken his words and fashioned them into a battle standard. This goes back at least as far as Shakespeare, who had Hamlet say the purpose of acting “was and is, to hold as ‘twere the mirror up to nature – to show virtue her feature, scorn her own image, and the very age and body of the time his form and pressure”.

Things are more complicated today. We live in the most self-reflecting age in history – what need do we have for art to hold a mirror up to life when our lives are already great interlocking halls of mirrors, of exams and televisual reality and Facebook and performance reviews? Post-modernism, too, has torn through theatre’s claim to play a role in shaping society through its own reflection. What can writers tell us about ourselves that we didn’t know already? What is left for theatre to do except confuse and entertain?

And so we come to Martin Crimp. Monastic, curmudgeonly, deliberately and defiantly obscure, Crimp is in a sense one of the last major playwrights of the old school. A man with a mirror. And he does not like what he sees. Not one little bit.

His plays are wild, furious, disorientating assaults on the modern world, its pettiness, its vanity, its distance from history, and above all its stupid, complacent, cow-eyed theatre-goers. Crimp captures everything with his mirror – your pretensions, your blind spots, your inanely grinning face, your empty laughter – and smashes the mirror, then recomposes the jagged little shards into a pitiless collage of absurdity.

His latest play, In the Republic of Happiness, is a glass-crunching prosecution of the twenty-first century. It opens with a family sitting down to Christmas dinner, with the safety catch off. One teenage daughter is pregnant, the other resentful; the mother is stifling, the father is chafing, his mother is caustic and his father is in a pompous fug of self-delusion.

They talk with no filters. “D’you think this bird’s been properly cooked?” the father says. “It’s just that ever since we started this meal I’ve felt a bit sick.” The bird has been properly cooked. “Then why does my mouth taste of vomit?” “It can’t be the bird, Tom.” “Well in that case it must be my particularly selfish daughter bringing up yet again the subject of her unplanned and ill-conceived pregnancy in front of this whole family when she can’t even name the father.”

A modern comedy of manners, the audience thinks. How biting, how daring, what fun. They relax, titter, and settle back in their seats. And just when they’re comfortable, Crimp attacks. Enter Uncle Bob, a menacingly mild presence come in from the cold like the Angel Gabriel. He brings a message from his wife.

“Basically this is the only opportunity she has,” he says, deprecating, “before we both leave – before we both irreversibly vanish – for her to tell you how much she hates you. Yes, hates you and abhors this family.” Each person round the table is flayed in turn. The titters grow nervous, then die faintingly away.

“She finds each one of you in your own way abhorrent,” Bob explains apologetically. “But it’s deeper than that, it’s deeper than that, it goes much deeper than that because it affects her physically – affects her skin – so even now – out there in the car – she’s having to rub in cream. She abreacts. You’re actually affecting – yes – fact – her ability to breathe.”

Round two: the lights crash out, and Bob’s wife enters, streaking straight into the bathroom and emerging in a dress so aggressive it can only be described as a declaration of war on reality. “Feels like I’m zipped into my own vagina.” She seizes the stage and sings over a thumpingly awful backing track dredged out of the benthic depths of 1980s synth pop (Dominic Cooke's effortlessly alive production uses these songs as bookends throughout).

The scene changes, and Crimp turns his mirror on the audience. The walls fall away, replaced by the set of a dated chat show. Its subject: our five essential freedoms. The freedom to take charge of your life, to treat your body as an object, to dwell on your past and its horrors, to assimilate your past into adult life, to progress into eternity, getting forever better – they are all swaddled in a thick latex skin of irony and suffocated, one by one.

The actors – no longer characters, but broken voices from a mewling ultramodern superego – chatter away in an inane and tessellating series of truisms. You want to laugh, you do laugh, but Crimp is always checking you, thrusting your own grotesque image in your face, explicitly if he has to. “I don’t talk in code,” one of the voices insists. “I don’t say I’m happy to separate my legs so that people who’ve been educated in a certain way or have particular beliefs can sit here in this audience and think that I mean the opposite – no way.”

The soundbites echo each other, pathetically, breaking down into rhymes and trashy songs and recurring non-sequiturs, interrupted by Crimp’s trademark device of stopping the flow of speech with meaningless emphases – “what / plus / look / yes / fact”.

And, gloriously, archaically, Crimp uses this violent, fracturing pastiche of everything you are to make a point: you are not an individual, you are a derivative product of history, weak, absurdly confident in a set of freedoms that are not really freedoms at all. As Irvine Welsh said, same fucking rules apply. You are no more in control of your life than anybody has ever been, you are governed by the same age-old, throbbing, intransigent forces and passions that have governed people since there were people, and, above all, right and wrong are very, very real.

But it goes deeper than that. Behind all this is a bolder message: theatre can and should have a point. It should have a sense of moral direction, and prove relativism wrong by example. Theatre should matter. Fifteen years ago, in Attempts on her Life, Crimp had one of his characters say: “It’s theatre - that’s right – theatre for a world in which theatre itself has died.” Strip away the layers of cruel irony, and it might be the voice of the author.

Crimp is no rampant Stuckist, no conservative: his work is a logical progression from the European modernists he has translated, masters of detachment and unreality like Ionesco and Genet. But he does abhor, in an old-fashioned way, what he sees as a vacuum of meaning.

The modern stage does many things well – it caricatures, it moves, it challenges, it shoves the brain and the heart into things the viewer never realised they could think and feel – but all but a handful of writers have lost the ability and desire to change societies. When plays do hit the headlines, it is because they tell us things we know already – Laura Wade’s Posh sending up the arrant whimsies of a class brought into the world to rule, or Jez Butterworth’s Jerusalem with its soothing song of an atavistic England.

There are glaring exceptions to this crude thesis, and the reasons for the decline of theatre’s influence over the way Britain thinks are a matter for another day, but it is a trend, and a trend that increasingly influences the way playwrights write. Crimp probably won’t change that. But he definitely won’t stop trying.

Five stars

In the Republic of Happiness is on at the Royal Court Theatre until January 19 2013. Tickets are £28/20/12