Duck test

A mallard, shown looking like a duck and swimming like a duck.

The duck test is a frequently cited colloquial example of abductive reasoning. Its usual expression is:

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 arguments that something might not be what it appears to be.

Notable uses

Indiana poet James Whitcomb Riley (1849–1916) may have coined the phrase when he wrote:

When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck. ^[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. But when I see a bird that quacks like a duck, walks like a duck, has feathers and webbed feet and associates with ducks—I'm certainly going to assume that he is a duck. ^[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. This bird has no label that says 'duck'. But the bird certainly looks like a duck. Also, he goes to the pond and you notice that he swims like a duck. Then he opens his beak and quacks like a duck. Well, by this time you have probably reached the conclusion that the bird is a duck, whether he's wearing a label or not. ^[3]

Elephant test

See also: Blind men and an elephant, Elephant in the room, and Seeing the elephant

"Hard to describe, but instantly recognizable when spotted"

Similarly, the term elephant test refers to situations in which an idea or thing, "is hard to describe, but instantly recognizable when spotted". ^[12]

The term is often used in legal cases when there is an issue which may be open to interpretation, ^{[13] [14]} such as in the case of Cadogan Estates Ltd v Morris, when Lord Justice Stuart-Smith referred to "the well known elephant test. 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." Overruling in part R v Ghosh. ^[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. He stated that the Constitution protected all obscenity except "hard-core pornography". 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. But I know it when I see it, and the motion picture involved in this case is not that."

See also

• Call a spade a spade  – Figurative expression
• Duck typing  – Style of dynamic typing in object-oriented programming
• Extensionality  – Logic principle
• I know it when I see it  – Colloquial expression
• Identity of indiscernibles  – Impossibility for separate objects to have all their properties in common
• Inductive reasoning  – Method of logical reasoning
• Operational definition  – Defining a concept in terms of specific, replicable actions or procedures, Despite the controversial
• Philosophical razor  – Principle that allows one to eliminate unlikely explanations
• Sympathetic magic  – Type of magic based on imitation or correspondence
• Zebra (medicine)  – Exotic diagnosis in medicine which is usually unnecessary and wrong

References

1. Heim, Michael (2007). Exploring Indiana Highways. Exploring America's Highway. p. 68. ISBN   978-0-9744358-3-1.
2. Sentinel, John (September 29, 1946). "Communist Expose The Case of the Duck". Milwaukee (WI) Sentinel.
3. Immerman, Richard H. (1982), The CIA in Guatemala: The Foreign Policy of Intervention, Austin, Texas: University of Texas Press, p. 102
4. Denver, Joseph; Ethel Franklin Betts (1965), Cushing of Boston: A Candid Portrait
5. Platt, Suzy (1992). Respectfully quoted. Library of Congress, Congressional Research Service. ISBN   978-0-88029-768-4."Attributed to Richard Cardinal Cushing. Everett Dirksen and Herbert V. Prochnow, Quotation Finder, p. 55 (1971). Unverified."
6. Adams, Douglas (1987). Dirk Gently's Holistic Detective Agency . Simon and Schuster. ISBN   978-0-671-62582-5.
7. Monty Python (1975). Monty Python and the Holy Grail.
8. Seipel, Tracy (March 19, 2015). "California drops hammer on Blue Shield tax-exempt status". San Jose Mercury News . Retrieved March 19, 2015.
9. Bailey, Derick. "SOLID Development Principles – In Motivational Pictures".
10. Melvin, Don; Cullinane, Susannah; Tawfeeq, Mohammed (October 1, 2015). "Russia's Lavrov on Syria targets: 'If it looks like a terrorist, walks like a terrorist ...'". CNN. Retrieved 9 July 2016.
11. Vladimir Vapnik: Statistical Learning an MIT Artificial Intelligence (AI) Podcast
12. Valuing and Judging Partners — Beyond the Elephant Test! Archived 2013-06-03 at the Wayback Machine , Edge International Review, Summer 2006
13. B.Wedderburn, The Worker and the Law (3rd ed, Harmondsworth, Penguin,1986), 116.
14. Catherine Barnard, The Personal Scope of the Employment Relationship Archived 2013-01-26 at the Wayback Machine , in T.Araki and S.Ouchi (eds), The Mechanism for establishing and Changing Terms and Conditions of Employment/The Scope of Labor Law and the Notion of Employees, The Japan Institute for Labour Policy and Training Report, 2004, vol.1, 131-136.
15. Cadogan Estates Ltd v Morris; EWCA Civ 1671 (4 November 1998) (at paragraph 17)
16. Ivey v Genting Casinos (UK) Ltd t/a Crockfords; [2017] UKSC 67 (25 Oct 2017) (at paragraph 48)

Further reading

• Christy, Howard Chandler; Betts, Ethel Franklin (1982), The complete works of James Whitcomb Riley