Determining the validity or truth of an idea or statement isn’t always easy and never has been easy. A fourteenth-century philosopher William of Occam had a useful rule of thumb for this quandary. We now know it as Occam’s Razor, and it is often stated thusly: “The simplest explanation is usually the best.”
The original Latin –“Pluralitas non est ponenda sine necessitate” — adds a wrinkle. This translates roughly, “Multiple variables are not to be posited without necessity.”
A more modern form of this principle is called the Duck test which is a humorous term for a form of inductive reasoning. This is its usual expression: If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.
The test implies that a person can identify an unknown subject by observing that subject’s habitual characteristics. It is sometimes used to counter abstruse, or even valid, arguments that something is not what it appears to be.