I generally follow Johnson’s advice never to respond to critics, but this is the season for breaking resolutions. So let me offer a brief rejoinder to Charles Barzun’s response to the Posner/Vermeule paper on the Inside/Outside Fallacy; both are recently published by the University of Chicago Law Review.
Eric and I suppose that successful arguments (in constitutional theory, inter alia) must pass through two separate, independent and cumulative filters: (1) a requirement of logical consistency (the inside/outside fallacy is one way of violating this requirement); (2) a requirement of substantive plausibility (not ultimate correctness).
With respect to some of the particular arguments we discuss in the paper, we say that the argument is caught in a dilemma — it can survive filter (1) only by taking a form that causes it to be weeded out by filter (2). Now in some of those cases, I take it, Charles disagrees with us that the argument fails the second filter. He is of course entitled to his views about that. But the inside/outside fallacy — which is the first filter — is strictly about the logical consistency of assumptions, not their plausibility. Thus the fallacy has already dropped out by that point; it is not affected at all by whatever happens in the debate at the second stage. It’s just a muddle to say that because Eric and I do happen to have substantive views about what counts as plausible for purposes of the second filter, we are therefore smuggling substantive content into the first filter. Not so — unless one subscribes to the postmodern view that logical consistency is itself a substantive requirement, thereby jettisoning the distinction between validity and truth. (In some passages, Charles seems willing to abandon himself utterly to that hideous error, but for charity’s sake we ought not read him so, if we can help it).
So when Charles says that the inside/outside fallacy smuggles in substantive assumptions, I think that’s a confusion that arises from failing to understand the distinction between the two filters. The reader of Charles’s piece should be alert for skipping to and fro between these distinct questions of logical consistency and plausibility.
(And see Eric’s earlier reply.)