Once a computer was asked, "What is the truth?" It took a very long time before the reply came, "I will tell you a story …"

Today, this is the only way I can answer the question I've been asked so often: "Why don't you write about A Midsummer Night's Dream? You must have so much to say!"

So – I'll tell you a story.

When I was 18 or 19, my one ambition was to make a film. By chance, I met the most eminent producer of the day, Sir Alexander Korda, a Hungarian of humble origins who had emigrated to make his fortune first in France, then in Britain, where he rose to power, was ennobled by the King and married a beautiful star, Merle Oberon, who for my father was "the perfect woman".

I had just been on a trip to Seville during Holy Week, was thrilled by the multitude of mysterious impressions and imagined a story set in this extraordinary background.

"Sir Alexander," I began, "I have an idea for a film – "

He cut me off with an unforgettable phrase that contained in a few words the period in which it was uttered, the British class system and the snobbery of a newly enlisted member of the upper classes. With a light dismissal of the hand he said: "Even a cook can have an idea."

This was virtually the end of the meeting. "Come back when you have developed your 'idea' enough to have a real story to offer me."

It took many years to free his phrase from its period and context and to hear the deep truth it contained.

This brings me directly to A Midsummer Night's Dream. It had never occurred to me to think of directing the Dream. I had seen many charming productions with pretty scenery and enthusiastic girls pretending to be fairies. Yet, when I was invited to do the play in Stratford, I discovered to my surprise that my answer was "Yes". Somewhere in me there was an intuition that I had ignored.

Then, the first visit to Europe of the Peking Circus revealed that in the lightness and speed of anonymous bodies performing astonishing acrobatics without exhibitionism, it was pure spirit that appeared. This was a pointer to go beyond illustration to evocation, and I began to imagine a co-production with the Chinese. A year later, in New York, it was a ballet of Jerome Robbins that opened another door. A small group of dancers around a piano brought into fresh and magical life the same Chopin nocturnes that had always been inseparable from the trappings of tutus, painted trees and moonlight. In timeless clothes, they just danced. These pointers encouraged a burning hunch that, somewhere, an unexpected form was waiting to be discovered.

I talked this over with Trevor Nunn, director of the Royal Shakespeare Theatre, who said for this season he had created a young company who could in no time learn anything that was needed. It seemed too good to be true, especially as the Chinese Circus acrobats started their training at the age of five.

So we began with only the conviction that if we worked long, hard and joyfully on all the aspects of the play, a form would gradually appear. We started preparing the ground to give this form a chance. Within each day we improvised the characters and the story, practised acrobatics and then passing from the body to the mind, discussed and analysed the text line by line, with no idea of where this was leading us. There was no chaos, only a firm guide, the sense of an unknown form calling us to continue.

Through freedom and joy, Alan Howard as Oberon not only found very quickly that he could master the art of spinning a plate on a pointed stick but that he could do so on a trapeze without losing any of the fine nuances of his exceptionally sensitive verse-speaking. His Puck, John Kane, did the same, while mastering walking on stilts. In another register, a very talented and tragically short-lived young actor, Glynne Edwards, discovered that all the accepted ideas of Thisbe's lament over Pyramus's death being a moment of pure farce were covering a true depth of feeling. This suddenly turned the usually preposterous attempts at acting of the "mechanicals" in the palace into something true and even moving. The situation was reversed and the smart and superior sniggering of the cultivated spectators well deserved the Duke's rebuke:

For never anything can be amiss

When simpleness and duty tender it.

Then, for the first time, we used a practice that we can no longer do without. In the middle of rehearsals, we invited a group of kids into our rehearsal room; then later we asked an ad-hoc crowd in a Birmingham social club, so as to test what we were doing. Immediately, strengths and lamentable weakness were pitilessly exposed. We saw the trap of rehearsal jokes – everything that made the company fall about with laughter fell flat. It was clear that some embryonic forms could be developed and others discarded, although in the process nothing was lost. One thing can always lead to another. On French level crossings there is an apt warning: "One train can conceal another." This can have a hopeful reading: "Behind a bad idea a good one can be waiting to appear."

Gradually, the jigsaw began to fit, yet the very first preview was a disaster. My old friend Peter Hall took me by the arm and expressed his regret at the bad flop that was on its way. But at this point in the process a shock was needed. What to do? Peter Hall's close collaborator John Barton said, "The problem is at the start. The way you begin doesn't prepare us for the unexpected approach that follows. As it is now, we just can't get into it." Thanks to John, we found a way of starting the play literally with a bang. With an explosion of percussion from the composer Richard Peaslee, the whole cast literally burst onto the stage, climbed up the ladders and swarmed across the top level of the set with such joy and energy that they swept the audience along with them. After this, they could do no wrong. The presence of the audience in a week of previews and a high-pressured re-examination of every detail allowed at last the latent form to appear. Then, like the well-cooked meal, there was nothing to fiddle with, just to taste and enjoy. Often, after an opening, one has to go on working day after day, never satisfied, but this time we could recognise it. Miraculously it had fallen into place.

When the production had played across the world, there were many proposals to film it. I always refused because the essence of designer Sally Jacobs's imagery was a white box. The invisible, the forest, even the darkness of night were evoked by the imagination in the nothingness that had no statement to make and needed no illustration. Unfortunately, the cinema of the day depended entirely on celluloid, and after the first screenings more and more scratches would appear. In any event, photography is essentially naturalistic and a film based only on whiteness, least of all a soiled and blotchy one, was unthinkable. Of course, a play can be filmed, but not literally. I've attempted this many times, and always a new form had to be found to correspond with a new medium. It can never be a literal recording of what the audience in the theatre once saw. Here I felt that nothing could reflect the zest and invention of the whole group. This truly was a live event.

Then the production was invited to Japan. Everyone was eager to go. As the costs were so high, could I agree to it being tele-recorded in performance so that it could be shown all over Japan and so contribute to their expenses? If we all agreed, they promised the recording would be destroyed in the presence of the British Consul. I discussed this with the cast, who had all been with me in refusing filming. This time it seemed impossible for us to say "No".

A few weeks later, I received a bulky parcel from Japan. It contained a set of large discs. "This," wrote one of the producers, "is a copy of the recording. We feel that you should have it."

I found a player and discovered to my amazement that it looked very good. I sent a cable to Japan, telling them not to destroy the master. At once a telegram returned. "This morning, in the presence of the British Consul, as you requested, the recording and the negative have been burned."

Only later did I realise that this was a valuable reminder to stay with my own convictions. The life of a play begins and ends in the moment of performance. This is where author, actors and directors express all they have to say. If the event has a future, this can only lie in the memories of those who were present and who retained a trace in their hearts. This is the only place for our Dream. No form nor interpretation is for ever. A form has to become fixed for a short time, then it has to go. As the world changes, there will and must be new and totally unpredictable Dreams.

Today, more than ever, I am left with a respect for the formless hunch which was our guide, and it has left me with a profound suspicion of the now much-used word "concept". Of course, even a cook has a concept, but it becomes real during the cooking, and a meal is not made to last. Unfortunately, in the visual arts, "concept" now replaces all the qualities of hard-earned skills of execution and development. In their place, ideas are developed as ideas, as theoretical statements that lead to equally intellectual statements and discussions in their place. The loss is not in words but in the draining away of what only comes from direct experience, which can challenge the mind and feeling by the quality it brings.

A used carpet placed over a mass of old, used shoes won international prizes. It was considered enough to express the tragedy of emigrations, of displaced people and their long march. This made an admirable piece of political correctness, but its impact was negligible when compared with Goya, Picasso or many shockingly intense photographs. A single lightbulb going on and off won an important award because it expressed all of life and death. In fact, it only expressed the "idea" of life and death. These have been prize-winning concepts, but would not Alexander Korda rightly have said, "Come back when you have put your idea into a powerful form"?

A form exists on every visible and invisible level. Through the quality of its development, then in the way its meaning is transformed. It is an understandable difficulty for actors, directors and designers facing a play of Shakespeare not to ask, "What should we do with it?" So much has been done already and so often filmed, recorded or described that it is hard not to begin by searching for something striking and new. A young director's future may depend on the impact he or she makes. It is hard to have to play characters like Rosencrantz and Guildenstern without looking desperately for an idea. This is the trap opening under the feet of every director. Any scene in Shakespeare can be vulgarised almost out of recognition with the wish to have a modern concept. This easily leads to spicing the words by having a drunk say them into a mobile phone or else peppering the text with obscene expletives. This is no exaggeration. I saw the videotape of an actor trying vainly to find a new way of saying "To be or not to be". As a last resort, one evening he set out to see whether alcohol might not be the answer. So he set up a camera, put a bottle of whisky on a table beside him, also a clock, and at planned intervals during the night recorded himself doing the soliloquy again and again as he gradually poured the contents of the bottle down his throat. The result needs no comment. Fortunately, there is another way. Always, an ever-finer form is waiting to be found through patient and sensitive trial and error. Directors are asked, "What is your concept?" The critics write about "a new concept" as though this label could cover the process. A concept is the result and comes at the end. Every form is possible if it is discovered by probing deeper and deeper into the story, into the words and into the human beings that we call the characters. If the concept is imposed in advance by a dominating mind, it closes all the doors.

We can all have an idea, but what can give the dish its substance and its taste?