A “white horse case”

According to A Dictionary of Modern Legal Usage by Bryan A. Garner, the term “white horse case” (not to be confused with the White Horse Dialogue) means a reported case with facts virtually identical to those of the instant case, so that the disposition of the reported case must determine the outcome of the instant case. This kind of case is also known under the terms horse case, gray mule case, goose case, and pony case.

A story that goes along with the white horse case takes place around the turn of the century in a Texas law firm.  There was a case in which a white horse owned by the client’s taxi service reared in the street, causing an elderly woman to fall and injure herself. The partner handling the case asked a young associate to find a case on point. The associate came back several hours later with a case involving an elderly lady who had fallen in the street after a taxi company’s black horse had reared in front of her. When the associate took this case to the partner, the partner said, "Nice try, son. Now, go find me a white horse case.".