The grid is useful in analyzing the Muller-Lyer visual illusion, which is perhaps the most famous of all visual illusions. In this illusion, two straight and parallel line segments of equal length are embedded in a 'context' that makes one of them appear long than the other. Imposing an appropriate grid on the figure is one way to provide an argument for why the two lines must be of equal length, even though they do not appear equal. In the law of evidence, the theory of decisionmaking under uncertainty provides a kind of grid underlying the choices that are made. Decisionmaking provides the law with a framework for setting policies, rather than with an aid in reaching verdicts in specific cases, however. Three legal issues that clarify the concept of a 'grid' are those of standards of proof, inadmissible evidence, and preventive detention. Many other legal phenomena could also be viewed from this grid. Drawings and 13 references.