The duck test is a humorous term for a form of inductive reasoning

Inductive reasoning

Inductive reasoning, also known as induction or inductive logic, is a kind of reasoning that constructs or evaluates propositions that are abstractions of observations. It is commonly construed as a form of reasoning that makes generalizations based on individual instances...

. This is its usual expression:
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 is not what it appears to be.

History

Indiana

Indiana

Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...

 poet James Whitcomb Riley

James Whitcomb Riley

James Whitcomb Riley was an American writer, poet, and best selling author. During his lifetime he was known as the Hoosier Poet and Children's Poet for his dialect works and his children's poetry respectively...

 (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." The phrase may also have originated much later with Emil Mazey, secretary-treasurer of the United Auto Workers

United Auto Workers

The International Union, United Automobile, Aerospace and Agricultural Implement Workers of America, better known as the United Auto Workers , is a labor union which represents workers in the United States and Puerto Rico, and formerly in Canada. Founded as part of the Congress of Industrial...

, at a labor meeting in 1946 accusing a person of being a communist.

The term was later popularized in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 by Richard Cunningham Patterson Jr., United States ambassador

Ambassadors from the United States

This is a list of ambassadors of the United States to individual nations of the world, to international organizations, to past nations, and ambassadors-at-large.Ambassadors are nominated by the President and confirmed by the Senate...

 to Guatemala

Guatemala

Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...

 during the Cold War

Cold War

The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

 in 1950, who used the phrase when he accused the Jacobo Arbenz Guzmán

Jacobo Arbenz Guzmán

Colonel Jacobo Árbenz Guzmán was a Guatemalan military officer and politician who served as Defense Minister of Guatemala from 1944–1951, and as President of Guatemala from 1951 to 1954....

 government of being Communist. Patterson explained his reasoning as follows:
Later references to the duck test include Cardinal Richard Cushing's, who used the phrase in 1964 in reference to Fidel Castro

Fidel Castro

Fidel Alejandro Castro Ruz is a Cuban revolutionary and politician, having held the position of Prime Minister of Cuba from 1959 to 1976, and then President from 1976 to 2008. He also served as the First Secretary of the Communist Party of Cuba from the party's foundation in 1961 until 2011...

.

Variants include Douglas Adams

Douglas Adams

Douglas Noel Adams was an English writer and dramatist. He is best known as the author of The Hitchhiker's Guide to the Galaxy, which started life in 1978 as a BBC radio comedy before developing into a "trilogy" of five books that sold over 15 million copies in his lifetime, a television...

' Dirk Gently's Holistic Detective Agency

Dirk Gently's Holistic Detective Agency

Dirk Gently's Holistic Detective Agency is a humorous fantasy detective novel by Douglas Adams, first published in 1987. It is described by "the author" on its cover as a "thumping good detective-ghost-horror-who dunnit-time travel-romantic-musical-comedy-epic".The book was followed by a sequel,...

:
The Liskov Substitution Principle

Liskov substitution principle

Substitutability is a principle in object-oriented programming. It states that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S without altering any of the desirable properties of that program...

 in computer science is sometimes expressed as a counter-example to the duck test:

See also

• Duck typing
  Duck typing
  In computer programming with object-oriented programming languages, duck typing is a style of dynamic typing in which an object's current set of methods and properties determines the valid semantics, rather than its inheritance from a particular class or implementation of a specific interface...
  
  
• Elephant test
  Elephant test
  The term elephant test refers to situations in which an idea or thing "is hard to describe, but instantly recognizable when spotted".- Uses :...
  
  
• I know it when I see it
  I know it when I see it
  The phrase "I know it when I see it" is a colloquial expression within the United States by which a speaker attempts to categorize an observable fact or event, although the category is subjective or lacks clearly defined parameters. The phrase was famously used by United States Supreme Court...
  
  
• Identity of indiscernibles
  Identity of indiscernibles
  The identity of indiscernibles is an ontological principle which states that two or more objects or entities are identical if they have all their properties in common. That is, entities x and y are identical if any predicate possessed by x is also possessed by y and vice versa...
  
  
• Occam's razor
  Occam's razor
  Occam's razor, also known as Ockham's razor, and sometimes expressed in Latin as lex parsimoniae , is a principle that generally recommends from among competing hypotheses selecting the one that makes the fewest new assumptions.-Overview:The principle is often summarized as "simpler explanations...
  
  
• To call a spade a spade
  To call a spade a spade
  To "call a spade a spade" is to speak honestly and directly about a topic, specifically topics that others may avoid speaking about due to their sensitivity or embarrassing nature. Brewer’s Dictionary of Phrase and Fable defines it as...
  
  
• Turing test
  Turing test
  The Turing test is a test of a machine's ability to exhibit intelligent behaviour. In Turing's original illustrative example, a human judge engages in a natural language conversation with a human and a machine designed to generate performance indistinguishable from that of a human being. All...
  
  
• Zebra (medical)
  Zebra (medical)
  Zebra is a medical slang term for a surprising diagnosis. Although rare diseases are, in general, surprising when they are encountered, other diseases can be surprising in a particular person and time, and so "zebra" is the broader concept....