Recursive

Recursive (pronounced ri-kur-siv)

(1) Pertaining to or using a rule or procedure that can be applied repeatedly; periodically recurring.

(2) Drawing upon itself, referring back.

(3) In mathematics, of an expression, each term of which is determined by applying a formula to preceding terms

(4) In computing, of a program or function that calls itself (often in the form of an endlessly repeating script).

(5) In computing theory, of a function which can be computed by a theoretical model of a computer, in a finite amount of time.

(6) In computing, a set whose characteristic function is recursive.

(7) In linguistics (as recursive acronym), an acronym in which the first letter of the first word represented by the acronym is the acronym itself.

1790: From the stem of Latin recursus, perfect passive participle of recurrō (I run or hasten back; I return, revert, recur), the construct being recurs(ion) + -ive.  The –ive suffix is from the Anglo-Norman -if (feminine -ive), from the Latin -ivus; the related forms are the adverb recursively and the noun recursiveness.  Until the fourteenth century, all Middle English loanwords from the Anglo-Norman ended in -if (actif, natif, sensitif, pensif et al) and, under the influence of literary Neolatin, both languages introduced the form -ive.  Those forms that have not been replaced were subsequently changed to end in -y (hasty, from hastif, jolly, from jolif etc).  Like the Latin suffix -io (genitive -ionis), the Latin suffix -ivus is appended to the perfect passive participle to form an adjective of action.  The use in mathematics dates from 1934.  Recursive is an adjective inflected form of recursion which is a noun.  Recursive is an adjective, recursivity & recursiveness are nouns and recursively is an adverb; the noun plural is recursivities.  

The recursive acronym

Although recursive acronyms had existed before, appearing in fiction as early as 1968, the term first gained wider attention when discussed in US physicist’s Douglas Hofstadter's (b 1945) 1979 book Gödel, Escher, Bach: an Eternal Golden Braid.  Recursive acronyms typically form backwardly: either an existing ordinary acronym is given a new explanation or, a name is turned into an acronym by giving the letters an explanation of what they stand for, in each case with the first letter standing recursively for the whole acronym.

Not an easy book for those without a helpful background, even the title of Gödel, Escher, Bach is at first glance misleading because it’s not a look at the relationships between art, music and mathematics but instead an exploration of the abstract structures which exist within each.  These Hofstadter called “strange loops”, the logician Kurt Friedrich Gödel (1906–1978) having demonstrated their existence in any mathematical system of sufficient complexity.

Relativity, lithograph (1953) by MC Escher (1898–1972).

Hofstadter pursued these structural imperatives in music and art, suggesting it’s strange loops which creates consciousness, the connections and chemicals in the human brain creating the fundamental base of the framework on which are hung ideas, feelings, hopes and desires, all of which manifest further up the framework.  Consciousness became possible (and there are those who suggested inevitable) because the hierarchy clinging to the framework can twist back on itself: higher and lower levels influencing and interacting so the lower which once must have entirely determined the upper is also changed, ideas and feelings having an actual physical impact, this tangling of hierarchies being our sense of self.

Others, tentatively had posed similar questions.  Eugene Charniak’s (b 1946) strangely neglected PhD thesis (MIT, 1974) at least hinted it might be fruitful to explore the relationship of knowledge and inference to natural language understanding and Gödel, Escher, Bach is a playful, clever, if sometimes obviously contrived way to offer one explanation of how cognition emerges from a mechanistic structure which is reflected in work that cognition can allow to be created.  As a technical point, remarkably for a piece so dependent on the nuances and interplay of language, Gödel, Escher, Bach has been translated.

Many recursive acronyms come from the field of computing; it’s nerd humor.

TLA: Three Letter Acronym

AROS: AROS Research Operating System

BAMF: BAMF Application Matching Framework

BIRD: BIRD Internet Routing Daemon

GNU: GNU's Not Unix

KGS: KGS Go Server

LAME: LAME Ain't an MP3 Encoder

MINT: MINT Is Not TRAC

MiNT: MiNT is Not TOS (which later became MiNT is Now TOS)

TIARA: TIARA is a recursive acronym

UIRA: UIRA Isn't a Recursive Acronym

WINE: WINE Is Not an Emulator (was originally Windows Emulator)

XINU: Xinu Is Not Unix

XNA: XNA's Not Acronymed

XNU: X is Not Unix