Begging the Queston

Yesterday's post was a bit long winded (by my standards) but the fuss over that paper has helped me refine my critique.

Never mind the economics or the maths, the problem I see in Reinhart and Rogoff is an error of logic. The idea of a 90% threshold is an assumption. It cannot therefore be a conclusion.

I can expose the logic using an old fashioned syllogism:
High debt correlates to low growth
The threshold for high debt is 90%                        
Therefore 90% debt is the threshold for low growth

If the premises are true so is the conclusion. R&R put a lot of effort into establishing the first premise but none at all into the second. It is an assumption.

Assuming your conclusions is the logical fallacy of begging the question, or as the ancients called it petitio principii. I have long supported the idea of teaching logic in schools. I now think it should be a compulsory subject for economists.