Duck test
The duck test is a frequently cited colloquial example of abductive reasoning.
[1]A common variation of the wording of the phrase may have originated much later with Emil Mazey, secretary-treasurer of the United Auto Workers, at a labor meeting in 1946 accusing a person of being a communist: I can't prove you are a Communist.
[2]The term was later popularized in the United States by Richard Cunningham Patterson Jr., United States ambassador to Guatemala in 1950 during the Cold War, who used the phrase when he accused Guatemala's Jacobo Arbenz Guzmán government of being Communist.
Patterson explained his reasoning as follows: Suppose you see a bird walking around in a farm yard.
Well, by this time you have probably reached the conclusion that the bird is a duck, whether he's wearing a label or not.
[4][5] Douglas Adams parodied this test in his book Dirk Gently's Holistic Detective Agency: If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family Anatidae on our hands.
[6]Monty Python also referenced the test in the Witch Logic scene in their 1975 film Monty Python and the Holy Grail: [Bedevere:] There are ways of telling whether she is a witch!
[7] In 2015, a variation of the duck test was applied in the revocation of tax exempt "nonprofit" status to Blue Shield of California:In a startling blow to one of California's biggest health insurers, the state has revoked the tax-exempt status of Blue Shield of California, forcing the company to pay tens of millions of dollars in back taxes and unleashing a torrent of calls for it to return billions of dollars to customers.
The tax board's action 'was an acknowledgment of what Blue Shield was already doing, or not doing,' said Anthony Wright, head of Health Access California, a consumer advocacy group.
[9]Russian Minister of Foreign Affairs Sergey Lavrov used a version of the Duck Test in 2015 in response to allegations that Russian airstrikes in Syria were not targeting terrorist groups, primarily ISIS, but rather West-supported groups such as the Free Syrian Army.
[10]Professor Vladimir Vapnik, a pioneer and co-inventor of Support Vector Machines (SVM) and a major contributor to the theory of machine learning and many foundational ideas in statistical learning, uses the duck test as a way to summarize the importance of simple predicates to classify things.
Similarly, the term elephant test refers to situations in which an idea or thing, "is hard to describe, but instantly recognizable when spotted".
It is difficult to describe, but you know it when you see it",[15] and in Ivey v Genting Casinos, when Lord Hughes (in discussing dishonesty) opined "like the elephant, it is characterised more by recognition when encountered than by definition."
[16] A similar incantation (used however as a rule of exclusion) was invoked by the concurring opinion of Justice Potter Stewart in Jacobellis v. Ohio, 378 U.S. 184 (1964), an obscenity case.
Stewart opined, "I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description; and perhaps I could never succeed in intelligibly doing so.
