"The primary criterion is excellence," the letter states.
Being first – the primary criterion for 24-hour news channels – is increasingly the least interesting and effective value they offer.
But skill is far from being the only, or even primary, criterion for what makes art art.
Identification seems to be the primary criterion, too, in his writing about literature.
At independent book chain Foyles, Jonathan Ruppin said he'd be backing Byatt to win, praising the judges for selecting a shortlist where "strong storytelling" seems to have been their primary criterion for inclusion.
If your primary criterion for success is economic performance per square metre, it's hard to beat the mostly immigrant micro-entrepreneurs that LSE ethnographer Suzi Hall studied in a project called Ordinary Streets.
It's an argument that won't be settled, but since I was asked this question on Saturday, a couple of hours after Phelps won his seventh gold medal of these Games, I began to contemplate what the primary criterion should be.
The bill prohibits the use of the number of arrests or citations issued by an officer as the sole or primary criterion for promotion, demotion, dismissal or the earning of any benefit.
The most controversial (and ridiculed) comment, however, came from another judge, former Labour MP Chris Mullin, who announced that his primary criterion was that the novels "had to zip along".
From ancient Athens to South Sudan, birth to certain parents, or in a certain territory, has been the primary criterion for citizenship.
The center has said that the primary criterion in the selection process is excellence and that the board of directors strives for balance across disciplines.
