“On all fours” is a metaphor used by legal practitioners to describe a previous case with facts that are substantially similar to the case at issue. The metaphor is meant as a comparison to an animal moving on all four legs. A case “on all fours” would establish effective legal precedent since it deals with nearly indistinguishable facts and issues as the other case. If facts in a precedent case are identical or reasonably similar to those in the compared case, the precedent is recognized as legitimate and it is applied.
The phrase is often used in a judicial opinion that discusses the doctrine of qualified immunity. Qualified immunity protects individuals acting in their official capacity from liability unless their actions violate a “clearly established right” that any reasonable person would have known. Judges have often said that when applying precedent, a case need not be on all fours with the facts at issue to form the basis of a “clearly established right” under qualified immunity analysis. This means that the facts do not need to be identical to establish clear precedent, but it must be well settled law so that every reasonable official would have understood that what he is doing violates the right in question.
[Last updated in August of 2020 by the Wex Definitions Team]