In my “Solipsist’s Guide to Comparative Advantage,” I showed how, for all practical purposes, trade actually raises worker productivity.  Notice, though, that my example shows the productivity effects of trade if you and I have different absolute advantages: you’re a better farmer, I’m a better steel-worker.  What about the case where you’re better at both jobs?  Such as:

 

Wheat

Steel

You

10

5

Me

1

2

For convenience, assume again that the wheat:steel price ratio is 1:1.

Then on the solipsistic assumption that I’m merely your tool, trade revises your productivity as follows:

Wheat

Steel

You

10

10

On the opposite assumption that you’re merely my tool, trade revises my productivity thusly:

Wheat

Steel

Me

2

2

Putting both perspectives together:  

 

Without Trade

With Trade

 

Wheat

Steel

Wheat

Steel

You

10

5

10

10

Me

1

2

2

2

Thanks to comparative advantage, trade allows you to effectively double your steel-making productivity, and allows me to effectively double my wheat-growing productivity.  And this is true despite the fact that I have absolutely nothing to teach you.