We can tell from a letter he wrote to his half-brother Domenico that Leonardo da Vinci never wanted a nephew. “My beloved brother,” it begins:
This is sent merely to inform you that a short time ago I received a letter from you from which I learned that you have an heir, which circumstance I understand has afforded you a great deal of pleasure. Now in so far as I had judged you to be possessed of prudence; I am now entirely convinced that I am as far removed from having accurate judgment as you are from prudence; seeing that you have been congratulating yourself on having created a watchful enemy, who will strive with all his energies after liberty, which can only come into being at your death.
You might put this sourness down to Leonardo’s illegitimacy. Remember the terse note with which he records his father’s death:
On the ninth day of July 1504, on Wednesday at seven o’clock, died, at the Palace of the Podestà, Ser Piero da Vinci, notary, my father, at seven o’clock; he was eighty years old, he left ten sons and two daughters.
As far as I can see, Leonardo is hereby excluding himself from the list of sons.
But illegitimacy might not be the only factor. Some artists have the desire to pass their skills on to a new generation, to sons or substitute sons; others want the line to end with them. Raphael, who had no sons, nevertheless surrounded himself with real artists younger than himself, at least half a dozen of them, who might be considered his sons. Vasari has him never leaving home surrounded by fewer than fifty artists. Michelangelo’s assistants, on the other hand, were mostly nonentities, and it seems clear that Michelangelo wanted the line to end with him, which is why he himself destroyed all the cartoons for the Sistine Chapel, and all the other working drawings he had with him in Rome at the end of his life.
Leonardo was disposed to gather around himself a court of young men—”L’Achademia Leonardi Vinci,” they called themselves—including the sons of noble families along with rather less reputable types. He wanted them to succeed in the arts for which he trained them, but none of them approached him in talent in the way that Giulio Romano could compare with Raphael. Perhaps he needed them for company as much as anything else. In Rome he complained that his young friends all deserted him, running off to play with the Swiss Guards among the ruins, hunting birds with slings. Leonardo took the view that it was a poor pupil who did not outstrip his master, just as he, in painting, had outstripped Verrocchio. If he thought of a son as a watchful enemy, this was perhaps because he knew what sort of son he had been.
Nevertheless, life went on. People took pleasure in producing sons and heirs. Ser …