Legal Definitions - fool's test

The fool's test was a method used by federal courts and the Federal Trade Commission to determine if an advertisement was deceptive. The test asked whether even a fool could believe the advertisement. The name comes from a passage in the Bible, Isaiah, which says "wayfaring men, though fools, shall not err therein." The test was first introduced in the case of Charles of the Ritz Distrib. Corp. v. Fed. Trade Comm'n in 1944.

For example, if an advertisement claimed that a pill could make a person lose 50 pounds in one day, the fool's test would ask whether even a fool would believe that claim. Obviously, no reasonable person would believe such a claim, so the advertisement would be considered deceptive.

The fool's test was replaced by the "reasonable consumer" test in 1984. This new test asks whether an advertisement would deceive a reasonable person, rather than a fool.