A Logic Puzzle for Phil

Slate's blog on legal issues.
July 1 2008 11:11 PM

A Logic Puzzle for Phil

An inventor has invented what he calls the M-Box. The M-Box is a lie detector and can be used to determine whether criminal suspects are lying or telling the truth. Unfortunately, the M-Box occasionally errs. Another inventor comes up with what he calls the C-Box. The C-Box is also a lie detector, and everyone understands that the C-Box could err as well. Suppose that someone makes a statement and the M-Box says "lie." Then a recording of that statement is played before the C-Box and the C-Box says "truth." Do we know that the M-Box is inaccurate because the C-Box disagrees with it?

Of course not. All we know is that the two contraptions disagree. We don't know which is correct in this instance, nor do we know which is more accurate in general. This is why Phil is wrong to say the D.C. Circuit opinion reversing the detention decision of a combatant status review tribunal proves that the tribunal is inferior to a court. All we learn from this incident is that the Military-Box and the Court-Box disagree.

Eric Posner, a professor at the University of Chicago Law School, is author of The Twilight of International Human Rights Law. Follow him on Twitter.

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