Ben Franklin's Prudential Algebra

I read a story in The New Yorker magazine ("The Art of Decision-making") a few years ago that I had filed away for some future blog post.  I was cleaning out some old stacks of papers the other day (remember the word "tsundoku"?) and came across it again.  The article starts with a story about how the famous naturalist Charles Darwin decided whether or not he would propose to his eventual wife, Emma Wedgwood.  Darwin was 29 years old at the time and had just returned 2 years earlier from his incredible voyage on the HMS Beagle, during which he had made a number of observations that would form the basis for his classic, On the Origin of Species.  Darwin worried that having a wife and children would slow down his scientific career.  

Darwin wrote down all of the pros and cons of marrying Ms. Wedgwood on a sheet of paper.  On the "con's" side of the paper, he listed points such as "loss of time", "anxiety and responsibility", "perhaps quarreling", and "cannot read in the evenings".  His "pro's" included, "children (God willing)", "constant companion (and friend in old age)"), and "home".  At the bottom, Darwin noted that "it would be intolerable to think of spending one’s whole life, like a neuter bee, working, working. . . ." and followed with, "Only picture to yourself a nice soft wife on a sofa with good fire and books and music perhaps."  On the bottom of his two lists, he wrote "Marry, Marry, Marry QED.”  He proposed to Ms. Wedgwood and they would spend the next 43 years together raising ten children.

Apparently, Benjamin Franklin had a similar method that he used whenever he needed to make a decision, which he called "moral or prudential algebra".  He recommended his approach to his good friend and fellow scientist, Joseph Priestley, the scientist who discovered oxygen, in the summer of 1772.  Priestley was struggling with a decision on whether to relinquish his position as the minister at Unitarian church Mill Hill Chapel in Leeds or accepting a lucrative position as the general assistant to the Earl of Shelburne.  

Franklin wrote, "...my way is to divide half a sheet of paper by a line into two columns; writing over the one pro, and over the other con. Then during three or four days consideration, I put down under the different heads short hits of the different motives, that at different times occur to me, for or against the measure."  

So far, Franklin's method seems a lot like Darwin's method above.  However, Franklin explained further, "When I have thus got them all together in one view, I endeavor to estimate their respective weights; and where I find two, one on each side, that seem equal, I strike them both out. If I find a reason pro equal to two reasons con, I strike out the three. If I judge some two reasons con, equal to some three reasons pro, I strike out the five; and thus proceeding I find at length where the balance lies, and if, after a day or two of further consideration, nothing new that is of importance occurs on either side, I come to a determination accordingly."

I've used both of these decision-making methods in the past, both when making important decisions on my own or as part of a group.  The weighting of particular pro's and con's is an important consideration, and one that should be agreed upon in advance (if the decision is to be made by a group).  Next time you are faced with an important decision, try using Franklin's prudential algebra to help you decide!