Those pesky negatives (revisited)

[Baker, John]

        I noticed a different issue with negatives today in Brad DeLong's Semi-Daily Journal, a popular economics blog:

        "You cannot--not given current projections--"support" all three of (a) diverting Social Security revenue to young workers' private accounts, (b) maintaining benefits at their current levels, and (c) keeping payroll taxes from rising."

        What struck me is that the meaning would be the same if he had written "You cannot--given current projections . . . ."  In his version, "not" is a double negative (with "cannot") that cannot be re-analyzed as a positive.

John Baker