(William B. Plowman/AP)

Why do we have a debt limit in the first place? We appropriate funds, we have tax law, and on reasonably adept at arithmetic can calculate what the debt change is going to be. The Congress and the president have signed legislation predetermining what that number is. Why we need suspenders and belts is something I’ve never understood.

Greenspan also makes the logical point that “you cannot have a position which stipulates that, ‘I will never allow the United States to default. But on the other hand, I will not allow the process to go forward unless there are additional actions with respect to the debt.’ ” In other words, if you’ve said you won't shoot the hostage, you can’t simultaneously demand a ransom.

Related: The Congressional Budget Office makes the case against the debt ceiling.