Unfortunately, Rincewind's memory was literally treacherous. It worked perfectly.

'So, then,' he said, wishing that he didn't have to, 'we didn't tell Will all that stuff?'

'What stuff?' said Ridcully.

'All about our magical library, for one thing. And you kept saying "Here's a good one, I bet you can use this" and you told him about those witches up in Lancre and how they got the new king on the throne, and that time the elves broke through, and how the Selachii and the Venturi families are always fighting—'

'We did?' said Ridcully.

'Yes. And about the countries we've visited. Lots of things.'

'Why didn't someone stop me?'

'The Dean did try. That's when you hit him with the Chair of Indefinite Studies, I think.'

The wizards sat in ale-smelling gloom.

'Should we have another try?' said the Lecturer in Recent Runes.

'What, and tell him to forget it all?' said Ridcully. 'Talk sense, man.'

'Perhaps we could go back in time and stop ourselves telling—'

'Don't say that! No more of that!' snapped the Archchancellor.

Rincewind pulled a copy of the play towards him. The wizards froze.

'Go on,' said Ridcully. 'Tell us the worst. What did he write?'

Rincewind opened the book and read a couple of lines at random:

'You spotted snakes, with double tongue; Thorny hedgehogs, be not—'

'No, no, no,' muttered the Dean, his head in his hands. 'Please tell me no one sang him the Hedgehog Song!'

Rincewind's lips moved as he read on. He turned over a few pages.

He flicked back to the beginning.

'It's all here,' he said. 'Same rather bad jokes, same unbelievable confusions, everything! Just as it was before! But it's going to happen here!'

The wizards looked at one another and dared to share a smug expression.

'Ah well, there we are then,' said Ridcully, sitting back. 'Job done.'

Rincewind turned some more pages. His recollections of the night were not coherent, but even a genius couldn't have made sense out of a bunch of drunken wizards all talking at once.

'Hex?' he said.

The crystal ball said: 'Yes?'

'Will this play be performed in this world?'

'That is the intention,' said the voice of Hex.

'And then what will happen?'

Hex told them, and added: 'That is one outcome.'

'Just a moment,' said Ponder Stibbons. 'There's more than one outcome?'

'Certainly. The play may not take place. Phase space contains a broadsheet account of a disruption of the first performance, followed by a fire in which a number of people died.

Subsequently the theatres were closed and the playwright died during a riot. He was struck by a pike.'

'You mean a halberd, of course,' said Ridcully.

'A pike,' Hex repeated. 'A fishmonger was involved.'

'What happened to civilisation?'

Hex was silent for a moment, and then said: 'Humanity failed by three years to leave the planet.'

LIES TO HUMANS

Please tell me no one sang him the Hedgehog Song ...

The Hedgehog Song, a Discworld ditty in the general tradition of Eskimo Nell, first made its appearance in Wyrd Sisters with its haunting refrain 'The hedgehog can never be buggered at all'.

The wizards have wielded the power of story with a vengeance. They have used it to prime their secret weapon, Shakespeare, and are convinced that he will prove more effective than a MIRVed ICBM. But before he's launched, they've very properly started to worry about collateral damage: possible cultural contamination by the Hedgehog Song.

It is a consequence only marginally less dire than eternal elf-infestation, but on the whole, preferable.

In the real Roundworld, the power of story is just as great as it is in the fictional counterpart.

Stories have power because we have minds, and we have minds because stories have power. It's a complicity, and all that remains is to unwrap it.

As we do so, bear in mind that Discworld and Roundworld are not so much different as complementary. Each, in its own estimation at least, gave birth to the other. On Roundworld, the Disc is seen as fantasy, the invention of an agile mind; Discworld is a series of stories

(amazingly successful) along with ceramic models, computer games and cassette tapes.

Discworld runs on magic, and on narrative imperative. Things happen on Discworld because people assume they will, and because some things have to happen to complete the story. From the standpoint of Roundworld, Discworld is a Roundworld invention.

The Discworld view is similar, but inverted. The wizards of Unseen University know that Roundworld is merely a Discworld creation, an unanticipated spin-off from an all-too-successful attempt to split the thaum and create the first self-sustaining magical chain reaction. They know this because they were there when it happened. Roundworld was deliberately created to keep magic out. Surprisingly, the magic-free vacuum acquired its own regulatory principle. Rules.

Things happen on Roundworld because they are consequences of the rules. However, it is astonishingly difficult to look at the rules and understand what their consequences will be. Those consequences are emergent. The wizards discovered this to their cost, as every attempt to do something straightforward in Roundworld - like creating life or jump-starting extelligence - went seriously awry.

These two worldviews are not mutually contradictory, for they are worldviews of two different worlds. Yet, thanks to the interconnectedness of L-space, each world illuminates the other.

The strange duality between Roundworld and Discworld parallels another: the duality between Mind and Matter. When Mind came to Roundworld, a very remarkable change occurred.

Narrative imperative appeared in Roundworld. Magic came into existence. And elves, and vampires, and myth, and gods. Characteristically, all of these things came into being in an indirect and offbeat way, like the relationship between rules and consequences. Things didn't exactly happen because of the power of story. Instead, the power of story made minds try to make the things in the story happen. The attempts were not always successful, but even when they failed, Roundworld was usually changed.

Narrative imperative arrived on Roundworld like a small god, and grew in stature according to human belief. When a million human beings all believe the same story, and all try to make it come true, their combined weight can compensate for their individual ineffectiveness.

There is no science in Discworld, only magic and narrativium. So the wizards put science into Discworld in the form of the Roundworld Project, as detailed in The Science of Discworld. With elegant symmetry, there was no magic or narrativium in Roundworld, so humans put them there, in the form of story.

Before narrative imperative can exist, there has to be narrative, and that's where Mind proved decisive. The imperative followed hard on the heels of the narrative, and the two complicitly coevolved, for as soon as there was a story, there was someone who wanted to make it come true.

Nonetheless, the story beat the compulsion by a nose.

What makes humans different from all other creatures on the planet is not language, or mathematics, or science. It is not religion, or art, or politics, either. All of those things are mere side effects of the invention of story. Now it might seem that without language there can be no stories, but that is an illusion, brought about by our current obsession with recording stories as words on paper. Before there was a word for 'elephant' it was possible to point at an elephant and make evocative gestures, to draw an elephant on the cave wall and add spears flying towards it, or to mould a model of an elephant from clay and act out a hunting scene. The story was as clear as day, and an elephant-hunt would follow hard on its heels.