Question: When I first learned about the term “orthogonal” in geometry class, it meant perpendicular. However, in recent years, I have noticed it being used in everyday English to mean “irrelevant.” How did this shift in meaning happen?
Answer: The original mathematical meaning of “orthogonal” has evolved over time, but the sense of it meaning “irrelevant” in everyday English is not very common and certainly not used on a daily basis.
The English adjective originated from Middle French, where orthogonal meant “having a right angle.” The term ultimately traces back to ancient Greek, where ὀρθογώνιος (orthogonios) meant “right-angled.”
The word first appeared in English in a 16th-century mathematical treatise, as documented in the Oxford English Dictionary. At that time, it also meant “right-angled.”
In the late 1600s, the OED notes that “orthogonal” took on a broader sense of “relating to or involving right angles; at right angles (to something else).”
Over the 19th and 20th centuries, it acquired various other mathematical meanings. However, one sense that emerged in the early 20th century – “statistically independent” – may be relevant to the newer, less common meaning of “irrelevant.”
This newer sense of “orthogonal” is defined by American Heritage online as “very different or unrelated; sharply divergent.” An example provided is: “Radical Islamists are ultimately seeking to create something orthogonal to our model of democracy” (from an article by Richard A. Clarke in The New York Times, Feb. 6, 2005).
Dictionary.com defines this sense as “having no bearing on the matter at hand; independent of or irrelevant to another thing or each other.” An example given is: “It’s an interesting question, but orthogonal to our exploration of the right to privacy.”
The OED, being an etymological dictionary, does not include this newer sense. It seems to have emerged in the late 20th century.
Examples of this newer sense include a statement by Terence McKenna in 1990 and a quote from Michael Shermer’s book Why People Believe Weird Things in 2002.
A notable use of “orthogonal” was seen in a discussion at the US Supreme Court in 2010, where the term was explained by University of Michigan law professor Richard Friedman to Chief Justice John Roberts and other justices.
(This account was compiled from reports in The Washington Post, the ABA Journal, The Volokh Conspiracy, and The BLT: The Blog of Legal Times.)
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