A commenter in “our previous post”:https://crookedtimber.org/2005/12/21/posner-forgets-himself/ points to “this chat session”:http://www.washingtonpost.com/wp-dyn/content/discussion/2005/12/20/DI2005122001142.html with Posner, hosted by the _Washington Post_. Besides forgetting everything he ever learned about public choice theory, Posner also seems to have abandoned the cost-benefit methods which made him famous. He is now convinced that radical uncertainty is not amenable to probabilistic analysis:
*Question*: … Nothing in the Constitution does (or could) provide a guarantee of safety. I suspect that I am statistically much more at risk of being run over by a car than of being killed by a terrorist (even though I live within five miles of the White House). Should the government ban all automobiles to protect me?
*Richard Posner*: If your premise were correct, your conclusion would follow. But how do you know you’re at less risk of being killed by a terrorist than being run down by a car? The risk in the sense of probability of being killed by a nuclear bomb attack on Washington, a dirty-bomb attack, an attack using bioengineered smallpox virus, a sarin attack on the Washington Metro (do you ever take the metro?), etc., etc., cannot be quantified. That doesn’t mean it’s small. For all we know, it’s great. Better safe than sorry.
How far this all is from the confidence with which Posner “typically slaps probabilities on things”:https://crookedtimber.org/2004/12/06/posner-and-becker-comedy-gold in order to justify some policy. Here he is arguing about preventive war in 2004:
Should imminence be an absolute condition of going to war, and preventive war thus be deemed always and everywhere wrong? Analytically, the answer is no. A rational decision to go to war should be based on a comparison of the costs and benefits … Suppose there is a probability of .5 that the adversary will attack at some future time, when he has completed a military build up, that the attack will, if resisted with only the victim’s current strength, inflict a cost on the victim of 100, so that the expected cost of the attack is 50 (100 x .5), but that the expected cost can be reduced to 20 if the victim incurs additional defense costs of 15. Suppose further that at an additional cost of only 5, the victim can by a preventive strike today eliminate all possibility of the future attack. Since 5 is less than 35 (the sum of injury and defensive costs if the future enemy attack is not prevented), the preventive war is cost-justified.
I guess his epistemological position has changed a great deal in the meantime. Incidentally, about “forty two thousand people a year”:http://www-fars.nhtsa.dot.gov/ are killed in automobile accidents in the United States. Do the math yourself.