Title somewhat misleading as the actual question asked in the post was 'safely borrow.' The more abstract question of 'how much' is of course infinite when the

Title somewhat misleading as the actual question asked in the post was 'safely borrow.' The more abstract question of 'how much' is of course infinite when there exists a compliant central bank that will 'buy' the debt and issue currency in return. The real world value of that currency would be expected to approach zero, in the limit. TANSTAAFL