So both in speech and in writing OK stands out clearly, easily distinguished from other words, and yet it uses simple sounds that are familiar to a multitude of languages.
Almost every language has an O vowel, a K consonant, and an A vowel. So OK is a very distinctive combination of very familiar elements. And that's one reason it's so successful. OK stands apart.
Ordinarily a word so odd, so distinctive from others, wouldn't be allowed in a language to begin with. As a general rule, a language allows new words only when they resemble familiar ones.
Metcalf's article briefly traces the development of the word, but also states his claim of its true origin:
On 23 March 1839, OK was introduced to the world on the second page of the Boston Morning Post, in the midst of a long paragraph, as "o.k. (all correct)".
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