Well, yes, if you *define* common as access to the same raw materials, labour and so on, then your conclusion follows. And I agree these are currently sacred cows. But to push the metaphor beyond reason, you could have got the cows from a different herd and as long as everyone agreed it would still be a common trading zone. For example, it doesn't seem beyond reason to me that in a decade or two we might mutually agree trade barriers as part of a strategy to reduce the environmental impact of transporting goods all over the place. Business would not be happy in the short term but would adapt to a more decentralised approach and carry on successfully.