It's pretty much the first part of any economics course. That moment when befuddled students are faced for the first time with those two crossed lines. The demand curve goes from the top left of the graph to the bottom right, the supply one from the bottom left to the top right. The insight about supply curves that we're expected to take away from this is that when prices rise, more people are happy to supply more of whatever good it is that has risen in price, when they fall, fewer.
Sadly, it would seem that our own government didn't quite make it to even this basic stage of the education system.
Official figures show that in 1996 there were 102,600 registered childminders in England, but the number had declined almost continuously to just 63,600 at the end of August this year.
Critics blame the 38 per cent drop on increased meddling from the Government and Ofsted, the education watchdog which carries out inspections.
By increasing regulation, increasing the registration fees that are payable, by increasing the amount of unpaid time that must be spent filling in forms rather than being paid to look after children, the government has reduced the price that childminders get for their labour. There are therefore fewer people willing to offer their services to look after children.
This isn't an arguable point, it's simply a statement of the obvious. But then it does so often take a government to ignore reality, doesn't it?
What leads to the desire to beat one's head on the table is that this was pushed through just as that same government decided that single parents should go back to work, leaving their children with the childminders who are no longer there.
Weren't we promised joined up government?