Five little Indian boys going in for law;
One got in Chancery and then there were four.
I'd read that many times, but it never really registered before: the reason the one gets subtracted from five is that courts of law and Chancery courts are different courts. Chancery courts are equity courts; they are concerned with remedy that falls short of grace or pardon (which historically is reserved to the Crown) but goes beyond (the historically much stricter) common law. So while Chancery is law in a very broad sense, the boy who gets appointed to the Court of Chancery leaves law in the narrow sense. I have read that rhyme many, many times, and it somehow never clicked, despite its being obvious if you know what 'Chancery' means. It's somewhat strange the way realizations come up sporadically and spontaneously, and things that did not click before suddenly one day just do.
In any case, it's easy to miss in the U.S., which still technically has the law/equity distinction, but whose equity courts and law courts have (except in a few jurisdictions) melded together, so that most American courts are equity courts with legal power (a reason for many complaints against them, actually, since courts of law have to apply law strictly but equity courts have quite expansive powers to create a remedy to fit the individual situation). This was a slow process, though. Thomas Jefferson has a letter from 1785 that gives a good summary of the differences between Chancery and law as it had been inherited by the United States (and also the argument for not uniting their functions).