There's no symmetry between having money and not having it, but the discussion had gone off the rails because everyone had assumed that there was, so that 'having money' was the opposite of 'having no money'. If you must find an opposite, then 'having money' is opposite to 'being in debt'. In that case, 'rich' is like 'knurd'. In any event, making the comparison between money, love, and air lowered the debating temperature considerably. Air isn't important if you've got it, only if you haven't; the same goes for money.
Vacuum is an interesting privative. Cut-me-own-Throat Dibbler could sell vacuum-on-a-stick. Vacuum in the right place is valuable.
Many people on Earth sell cold-on-a-stick.
Discworld does a marvellous job of revealing the woolly thinking behind our assumptions about absence, because in Discworld privatives really do exist. The dark/light joke in Discworld is silly enough that everyone gets the point, we hope. Other Discworld uses of privatives, however, are more subtle. The most dramatic, of course, is Death, many people's favourite Discworld character, who SPEAKS IN CAPITAL LETTERS. Death is a seven-foot-tall skeleton, with tiny points of light in his eye sockets. He carries a scythe with a blade so thin that it's transparent, and he has a flying horse called Binky. When Death appears to Olerve, king of Sto Lat, in Mort, it takes the king a few moments to catch up on current events:
'Who the hell are you?' said the king. 'What are you doing here? Eh? Guards! I deman...'
The insistent message from his eyes finally battered through to his brain. Mort was impressed. King Olerve had held on to his throne for many years and, even when dead, knew how to behave.
'Oh,' he said. 'I see. I didn't expect to see you so soon.'
YOUR MAJESTY, said Death, bowing, FEW DO.
The king looked around. It was quiet and dim in this shadow world, but outside there seemed to be a lot of excitement.
'That's me down there, is it?'
I'M AFRAID SO, SIRE.
'Clean job. Crossbow, was it?'
Our earthly fears about death have led to some of our strangest reifi-cations. Inventing the concept 'death' is giving a name to a process, dying, as if it's a 'thing'. Then, of course, we endow the thing with a whole suite of properties, whose care is known only to the priests. That thing turns up in many guises. It may appear as the 'soul', a thing that must leave the body when it turns it from a live body into a dead one. It is curious that the strongest believers in the soul tend to be people who denigrate material things; yet they then turn their own philosophy on its head by insisting that when an evident process, life, comes to an end, there has to be a thing that continues. No. When a process stops, it's no longer 'there'. When you stop beating an egg, there isn't some pseudo-material essence-of-eggbeater that passes on to something else. You just aren't turning the handle any more.
Another 'thing' that arises from the assumption that death exists is whatever must be instituted in the egg/embryo/foetus in order to turn it into a proper human being, who can die when required. Note that in human myth and Discworld reality it is the soulless ones, vampires and their ilk, who cannot die. Long before ancient Egypt and the death-god Anubis, priests have made capital out of this verbal confusion. On Discworld, it's entirely proper to have 'unreal' things, like Dark, or like the Tooth Fairy in Hogfather, which play their part in the plot. But it's a very strange idea indeed on planet Earth.
Yet it may be part of some process that makes us human beings. As Death points out in Hogfather, humans seem to need to project a kind of interior decoration on to the universe, so that they spend much of the time in a world of their own making. We seem, at least, at the moment, to need these things. Concepts like gods, truth and soul appear to exist only in so far as humans consider them to do so (although elephants are known to get uneasy and puzzled upon finding elephant bones in the wild, whether this is because of some dim concept of the Big Savannah In The Sky or merely because it's manifestly not a good idea to stay in a place where elephants get killed is unknown). But they work some magic for us. They add narrativium to our culture. They bring pain, hope, despair, and comfort. They wind up our elastic. Good or bad, they've made us into people.
We wonder if the users thought that that cold-focusing mirror worked some magic for them. We can think of several ways in which it might appear to. And some very clever friends of ours are persuaded that souls might exist, too. Nearly everything is a process on some level. To a physicist, matter is a process carried out by a quantum wave function. And quantum wave functions exist only when the person you're arguing with asserts that they don't, so maybe souls exist in the same way.
In this area, we have to admit the science doesn't know everything. Science is based on not knowing everything. But it does know some things.
NO POSSIBILITY OF LIFE
IT WAS DIFFICULT EATING SANDWICHES that you couldn't see. Rincewind was aware that back in the real world the Librarian was handing them to him, and he had to take it on trust that they were going to be cheese and chutney. As it turned out, he detected a hint of banana, too.
The wizards were shocked. It's terrible to find that you can't do what you like with your own universe.
'So we can't just magic life into the Project?' said the Dean.
Tin afraid not, sir,' said Ponder. 'We have quite a lot of control over things, but only in a very subtle way. I have gone into this'
'I don't call moving huge worlds very subtle,' said the Dean.
'In Project terms, even moving the moon into place took a hundred thousand years,' said Ponder. 'Time prefers to move faster in there. It's amazing what you can move if you give it a little push for that long.'
'But we've done so many things...'
'Just moved things around, sir.'
'Seems a shame to have made a world and there's no one to live on it,' said the Senior Wrangler.
'When I was small, I had a model farmyard,' said the Bursar, looking up from his reading.
'Thank you, Bursar. Very interesting,' said the Archchancellor. 'All right, let's play by the rules. What do you have to move around to get people?'
'Well ... bits of other people, my father told me,' said the Dean.
'Bad taste there, Dean.'
'Many religions start with dust,' said the Senior Wrangler. 'And then you bring it alive in some way.'
'That's pretty hard even with magic,' said the Archchancellor. 'And we can't use magic.'
'Up in Nothingfjord they believe that all life was created when the god Noddi cut off his ... unmentionables and hurled them at the sun, who was his father,' said the Senior Wrangler.
'What, you mean his ... underwear?' said the Lecturer in Recent Runes, who could be a bit slow.
'First of all we can't physically exist inside the Project, secondly that sort of thing is unhygienic, and thirdly I doubt very much if you'll find a volunteer,' said the Archchancellor sharply. 'Anyway, we're men of magic. That is superstition.'
'Can we make weather, then?' said the Dean.
'I think HEX can let us do that,' said Ponder. 'Weather is only pushing stuff around.'
'So we can aim lightning at anyone we don't like?'
'But there isn't anyone on the world, whether we like them or not,' said Ponder wearily. 'That's the point.'
'And while the Dean can make enemies anywhere, I think that, ah, Roundworldwould test even his powers,' said Ridcully.