When Charles Darwin set out to marry, he employed a technique pioneered half a century earlier by Ben Franklin. Despite his importance, the prolific Franklin often gave his practical wisdom to many of those who asked.
In the summer of 1772, Franklin received a letter from his friend, the English scientist, Joseph Priestley. Priestley was torn between relinquishing his position as the minister of the fame Unitarian church Mill Hill Chapel in Leeds and accepting a lucrative position as the general assistant to the Earl of Shelburne.
Like many of us faced with such a choice, Priestley was torn and turned to a friend for advice. Rather than simply offering advice on this particular choice, Franklin taught him something much more valuable: how to choose. By giving Priestley the simple mathematics of decision making, Franklin created what is now known as the pros and cons framework.
In the Affair of so much Importance to you, wherein you ask my Advice, I cannot for want of sufficient Premises, advise you what to determine, but if you please I will tell you how.
When these difficult Cases occur, they are difficult chiefly because while we have them under Consideration all the Reasons pro and con are not present to the Mind at the same time; but sometimes one Set present themselves, and at other times another, the first being out of Sight. Hence the various Purposes or Inclinations that alternately prevail, and the Uncertainty that perplexes us.
To get over this, 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 Hints of the different Motives that at different Times occur to me for or against the Measure. When I have thus got them all together in one View, I endeavour 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 some 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 Ballance lies; and if after a Day or two of farther Consideration nothing new that is of Importance occurs on either side, I come to a Determination accordingly.
And tho’ the Weight of Reasons cannot be taken with the Precision of Algebraic Quantities, yet when each is thus considered separately and comparatively, and the whole lies before me, I think I can judge better, and am less likely to take a rash Step; and in fact I have found great Advantage from this kind of Equation, in what may be called Moral or Prudential Algebra.
Priestley accepted the position and science never looked back.