Q From Jeffrey W. Frazier: The legal expression on all fours is defined in Black’s Law Dictionary, Fifth Edition, as ‘A phrase used to express the idea that a case at bar is in all points similar to another. The one is said to be on all fours with the other when the facts are similar and the same questions of law are involved’. But that raises the question — what is the origin of the phrase ‘on all fours’?
A The image behind it is that of a dog or similar animal. If it has use of all four legs, it runs smoothly and evenly, as opposed to the way it would limp if one of its legs were damaged. The expression was originally on all four, known from the sixteenth century in phrases we’re still familiar with, such as to crawl upon all four (the final “-s” was added in the nineteenth century; earlier, a word such as “legs” or “extremities” was understood).
In the eighteenth century, people started to use to run on all four as a figurative expression to describe some proposition or circumstance that was fair or equitable, well-founded, sturdily able to stand by itself. To be on all four or to stand on all four meant to be on a level with another, to present an exact analogy or comparison with something else (presumably the image is of two animals standing together, both on all four legs, hence in closely similar situations).
It’s hardly common now outside the legal profession, and I suspect from what subscribers have told me that it doesn’t turn up that often these days even in that field.