Double-Entry Bookkeeping
Books that must balance turned trade into something you could check. Pacioli writes in the Summa, in effect, that without double entry a merchant cannot sleep easy at night — do not go to bed until debits and credits agree. Goethe's line calling it «one of the finest inventions of the human mind» comes from Wilhelm Meister's Apprenticeship, Book I, Chapter 10 — and the praise is not an economist's but a character's, explaining commerce to a young man who wants to be a merchant. For the practice itself, look at what Francesco Datini of Prato left behind. In 1870, a disused stairwell in his old house gave up around 150,000 letters, more than 500 ledgers and account books, 300 partnership contracts and 400 insurance policies. Medieval commerce survived almost whole. Many pages of the ledgers are said to open with the words «In the name of God and of profit». This craft grew in the hands of people who did not separate faith from business. The paper colour of this map's Counting House room is taken from those books.
The myth, corrected
Pacioli invented double-entry bookkeeping
He did not invent it; he published it. The oldest surviving complete set of double-entry books belongs to the massari, the accountants of the city of Genoa, in 1340 — more than a hundred and fifty years before the Summa of 1494. Genoa had already required accounts to be kept «in the manner of the bankers» by a statute of 1327. The supposed inventor was the last person to write it down.