A Rational Argument

You are, by oc­cu­pa­tion, a cam­paign man­ager, and you’ve just been hired by Mor­timer Q. Sn­od­grass, the Green can­di­date for Mayor of Hadley­burg. As a cam­paign man­ager read­ing a book on ra­tio­nal­ity, one ques­tion lies fore­most on your mind: “How can I con­struct an im­pec­ca­ble ra­tio­nal ar­gu­ment that Mor­timer Q. Sn­od­grass is the best can­di­date for Mayor of Hadley­burg?”

Sorry. It can’t be done.

“What?” you cry. “But what if I use only valid sup­port to con­struct my struc­ture of rea­son? What if ev­ery fact I cite is true to the best of my knowl­edge, and rele­vant ev­i­dence un­der Bayes’s Rule?”1

Sorry. It still can’t be done. You defeated your­self the in­stant you speci­fied your ar­gu­ment’s con­clu­sion in ad­vance.

This year, the Hadley­burg Trum­pet sent out a 16-item ques­tion­naire to all may­oral can­di­dates, with ques­tions like “Can you paint with all the col­ors of the wind?” and “Did you in­hale?” Alas, the Trum­pet’s offices are de­stroyed by a me­te­orite be­fore pub­li­ca­tion. It’s a pity, since your own can­di­date, Mor­timer Q. Sn­od­grass, com­pares well to his op­po­nents on 15 out of 16 ques­tions. The only stick­ing point was Ques­tion 11, “Are you now, or have you ever been, a su­pervillain?”

So you are tempted to pub­lish the ques­tion­naire as part of your own cam­paign liter­a­ture . . . with the 11th ques­tion omit­ted, of course.

Which crosses the line be­tween ra­tio­nal­ity and ra­tio­nal­iza­tion. It is no longer pos­si­ble for the vot­ers to con­di­tion on the facts alone; they must con­di­tion on the ad­di­tional fact of their pre­sen­ta­tion, and in­fer the ex­is­tence of hid­den ev­i­dence.

In­deed, you crossed the line at the point where you con­sid­ered whether the ques­tion­naire was fa­vor­able or un­fa­vor­able to your can­di­date, be­fore de­cid­ing whether to pub­lish it. “What!” you cry. “A cam­paign should pub­lish facts un­fa­vor­able to their can­di­date?” But put your­self in the shoes of a voter, still try­ing to se­lect a can­di­date—why would you cen­sor use­ful in­for­ma­tion? You wouldn’t, if you were gen­uinely cu­ri­ous. If you were flow­ing for­ward from the ev­i­dence to an un­known choice of can­di­date, rather than flow­ing back­ward from a fixed can­di­date to de­ter­mine the ar­gu­ments.

A “log­i­cal” ar­gu­ment is one that fol­lows from its premises. Thus the fol­low­ing ar­gu­ment is illog­i­cal:

  • All rec­t­an­gles are quadrilat­er­als.

  • All squares are quadrilat­er­als.

  • There­fore, all squares are rec­t­an­gles.

This syl­l­o­gism is not res­cued from illogic by the truth of its premises or even the truth of its con­clu­sion. It is worth dis­t­in­guish­ing log­i­cal de­duc­tions from illog­i­cal ones, and to re­fuse to ex­cuse them even if their con­clu­sions hap­pen to be true. For one thing, the dis­tinc­tion may af­fect how we re­vise our be­liefs in light of fu­ture ev­i­dence. For an­other, slop­piness is habit-form­ing.

Above all, the syl­l­o­gism fails to state the real ex­pla­na­tion. Maybe all squares are rec­t­an­gles, but, if so, it’s not be­cause they are both quadrilat­er­als. You might call it a hyp­o­crit­i­cal syl­l­o­gism—one with a dis­con­nect be­tween its stated rea­sons and real rea­sons.

If you re­ally want to pre­sent an hon­est, ra­tio­nal ar­gu­ment for your can­di­date, in a poli­ti­cal cam­paign, there is only one way to do it:

  • Be­fore any­one hires you, gather up all the ev­i­dence you can about the differ­ent can­di­dates.

  • Make a check­list which you, your­self, will use to de­cide which can­di­date seems best.

  • Pro­cess the check­list.

  • Go to the win­ning can­di­date.

  • Offer to be­come their cam­paign man­ager.

  • When they ask for cam­paign liter­a­ture, print out your check­list.

Only in this way can you offer a ra­tio­nal chain of ar­gu­ment, one whose bot­tom line was writ­ten flow­ing for­ward from the lines above it. What­ever ac­tu­ally de­cides your bot­tom line is the only thing you can hon­estly write on the lines above.

1See “What Is Ev­i­dence?” in Map and Ter­ri­tory.