What do paper, printing with moveable type, gunpowder and the compass have in common? The answer is that they were Chinese inventions. Without them, the European advances from the 15th century onwards would have been far harder, if not impossible.

This story illustrates why we should want productive knowledge to flow across the world. Knowledge also “wants to be free” because unlike a commodity, my use of your idea does not prevent you, or anybody else, from using it. In the jargon, knowledge is “non-rival” in consumption, which gives it the character of a “public good”.

But creating that new idea may well have been costly. If you knew that I (and everybody else) could use it without compensation, you could be less inclined to develop the idea at all. This is a “free-rider problem”. Intellectual property rights exist to solve it, by creating a temporary monopoly in the idea.