linguistic:voice_change, information:extraction
Back-translation

A "back-translation" is a translation of a translated text back into the language of the original text, made without reference to the original text. Comparison of a back-translation with the original text is sometimes used as a check on the accuracy of the original translation, much as the accuracy of a mathematical operation is sometimes checked by reversing the operation. But the results of such reverse-translation operations, while useful as approximate checks, are not always precisely reliable. Back-translation must in general be less accurate than back-calculation because linguistic symbols (words) are often ambiguous, whereas mathematical symbols are intentionally unequivocal. In the context of machine translation, a back-translation is also called a "round-trip translation." When translations are produced of material used in medical clinical trials, such as informed-consent forms, a back-translation is often required by the ethics committee or institutional review board.

Mark Twain provided humorously telling evidence for the frequent unreliability of back-translation when he issued his own back-translation of a French translation of his short story, " The Celebrated Jumping Frog of Calaveras County ". He published his back-translation in a 1903 volume together with his English-language original, the French translation, and a "Private History of the 'Jumping Frog' Story". The latter included a synopsized adaptation of his story that Twain stated had appeared, unattributed to Twain, in a Professor Sidgwick's Greek Prose Composition (p. 116) under the title, "The Athenian and the Frog"; the adaptation had for a time been taken for an independent ancient Greek precursor to Twain's "Jumping Frog" story.

When a document survives only in translation, the original having been lost, researchers sometimes undertake back-translation in an effort to reconstruct the original text. An example involves the novel The Saragossa Manuscript by the Polish aristocrat Jan Potocki (1761–1815), who wrote the novel in French and anonymously published fragments in 1804 and 1813–14. Portions of the original French-language manuscript were subsequently lost; however, the missing fragments survived in a Polish translation, made by Edmund Chojecki in 1847 from a complete French copy that has since been lost. French-language versions of the complete Saragossa Manuscript have since been produced, based on extant French-language fragments and on French-language versions that have been back-translated from Chojecki's Polish version.

Many works by the influential Classical physician Galen survive only in medieval Arabic translation. Some survive only in Renaissance Latin translations from the Arabic, thus at a second remove from the original. To better understand Galen, scholars have attempted back-translation of such works in order to reconstruct the original Greek.

When historians suspect that a document is actually a translation from another language, back-translation into that hypothetical original language can provide supporting evidence by showing that such characteristics as idioms, puns, peculiar grammatical structures, etc., are in fact derived from the original language. For example, the known text of the Till Eulenspiegel folk tales is in High German but contains puns that work only when back-translated to Low German. This seems clear evidence that these tales (or at least large portions of them) were originally written in Low German and translated into High German by an over- metaphrastic translator.

Supporters of Aramaic primacy —the view that the Christian New Testament or its sources were originally written in the Aramaic language —seek to prove their case by showing that difficult passages in the existing Greek text of the New Testament make much more sense when back-translated to Aramaic: that, for example, some incomprehensible references are in fact Aramaic puns that do not work in Greek. Due to similar indications, it is believed that the 2nd century Gnostic Gospel of Judas, which survives only in Coptic, was originally written in Greek.

John Dryden (1631–1700), the dominant English-language literary figure of his age, illustrates, in his use of back-translation, translators' influence on the evolution of languages and literary styles. Dryden is believed to be the first person to posit that English sentences should not end in prepositions because Latin sentences cannot end in prepositions. Dryden created the proscription against " preposition stranding " in 1672 when he objected to Ben Jonson 's 1611 phrase, "the bodies that those souls were frighted from", though he did not provide the rationale for his preference. Dryden often translated his writing into Latin, to check whether his writing was concise and elegant, Latin being considered an elegant and long-lived language with which to compare; then he back-translated his writing back to English according to Latin-grammar usage. As Latin does not have sentences ending in prepositions, Dryden may have applied Latin grammar to English, thus forming the controversial rule of no sentence-ending prepositions, subsequently adopted by other writers.