The question of fidelity vs. transparency has also been formulated in terms of, respectively, "formal equivalence" and "dynamic equivalence." The latter two expressions are associated with the translator Eugene Nida and were originally coined to describe ways of translating the Bible, but the two approaches are applicable to any translation.
"Formal equivalence" corresponds to "metaphrase," and "dynamic equivalence", to "paraphrase."
"Dynamic equivalence" (or "functional equivalence") conveys the essential thought expressed in a source text — if necessary, at the expense of literality, original sememe and word order, the source text's active vs. passive voice, etc.
By contrast, "formal equivalence" (sought via "literal" translation) attempts to render the text "literally," or "word for word" (the latter expression being itself a word-for-word rendering of the classical Latin "verbum pro verbo") — if necessary, at the expense of features natural to the target language.
There is, however, no sharp boundary between dynamic and formal equivalence. On the contrary, they represent a spectrum of translation approaches. Each is used at various times and in various contexts by the same translator, and at various points within the same text — sometimes simultaneously. Competent translation entails the judicious blending of dynamic and formal equivalents.
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. In the context of machine translation, this is also called a "round-trip translation." It is analogous to reversing a mathematical operation; but even in mathematics such a reversal frequently does not produce a value that is precisely identical with the original.
Comparison of a back-translation to the original text is sometimes used as a quality check on the original translation. But while useful as an approximate check, it is far from infallible. Humorously telling evidence for this was provided by Mark Twain when he issued his own back-translation of a French version of his famous short story, "The Celebrated Jumping Frog of Calaveras County."
In cases when a historic 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). The polymath polyglot composed the book entirely in French and published fragments anonymously in 1804 and 1813–14. Portions of the original French-language manuscripts were subsequently lost; the missing fragments survived, however, in a Polish translation that was made by Edmund Chojecki in 1847 from a complete French copy, now 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.
Similarly, 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 many puns which only work if back-translated into Low German. This seems clear evidence that these tales (or at least large portions of them) were originally composed in Low German and rendered into High German by an over-metaphrastic translator.
Similarly, supporters of Aramaic primacy—i.e., of 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 better sense if back-translated into Aramaic—that, for example, some incomprehensible references are in fact Aramaic puns which do not work in Greek.
Translation of literary works (novels, short stories, plays, poems, etc.) is considered a literary pursuit in its own right. Notable in Canadian literaturespecifically as translators are figures such as Sheila Fischman, Robert Dickson and Linda Gaboriau, and the Governor General's Awards annually present prizes for the best English-to-French and French-to-English literary translations.
Other writers, among many who have made a name for themselves as literary translators, include Vasily Zhukovsky, Tadeusz Boy-Żeleński, Vladimir Nabokov, Jorge Luis Borges, Robert Stiller and Haruki Murakami.
The first important translation in the West was that of the Septuagint, a collection of Jewish Scriptures translated into Koine Greek in Alexandria between the 3rd and 1st centuries BCE. The dispersed Jews had forgotten their ancestral language and needed Greek versions (translations) of their Scriptures.
Throughout the Middle Ages, Latin was the lingua franca of the western learned world. The 9th-century Alfred the Great, king of Wessex in England, was far ahead of his time in commissioning vernacular Anglo-Saxon translations of Bede's Ecclesiastical History and Boethius' Consolation of Philosophy. Meanwhile the Christian Church frowned on even partial adaptations of the standard LatinBible, St. Jerome's Vulgate of ca. 384 CE.
In Asia, the spread of Buddhism led to large-scale ongoing translation efforts spanning well over a thousand years. The Tangut Empire was especially efficient in such efforts; exploiting the then newly-invented block printing, and with the full support of the government (contemporary sources describe the Emperor and his mother personally contributing to the translation effort, alongside sages of various nationalities), the Tanguts took mere decades to translate volumes that had taken the Chinese centuries to render.
Large-scale efforts at translation were undertaken by the Arabs. Having conquered the Greek world, they made Arabic versions of its philosophical and scientific works. During the Middle Ages, some translations of these Arabic versions were made into Latin, chiefly at Córdoba in Spain. Such Latin translations of Greek and original Arab works of scholarship and science would help advance the development of European Scholasticism.
The broad historic trends in Western translation practice may be illustrated on the example of translation into the English language.
The first fine translations into English were made by England's first great poet, the 14th-century Geoffrey Chaucer, who adapted from the Italian of Giovanni Boccaccio in his own Knight's Tale and Troilus and Criseyde; began a translation of the French-language Roman de la Rose; and completed a translation of Boethius from the Latin. Chaucer founded an English poetic tradition on adaptations and translations from those earlier-established literary languages.
The first great English translation was the Wycliffe Bible (ca. 1382), which showed the weaknesses of an underdeveloped English prose. Only at the end of the 15th century would the great age of English prose translation begin with Thomas Malory's Le Morte Darthur—an adaptation of Arthurian romances so free that it can, in fact, hardly be called a true translation. The first great Tudor translations are, accordingly, the Tyndale New Testament (1525), which would influence the Authorized Version (1611), and Lord Berners' version of Jean Froissart's Chronicles (1523–25).
Meanwhile, in Renaissance Italy, a new period in the history of translation had opened in Florence with the arrival, at the court of Cosimo de' Medici, of the Byzantine scholar Georgius Gemistus Pletho shortly before the fall of Constantinople to the Turks (1453). A Latin translation of Plato's works was undertaken by Marsilio Ficino. This and Erasmus' Latin edition of the New Testament led to a new attitude to translation. For the first time, readers demanded rigor of rendering, as philosophical and religious beliefs depended on the exact words of Plato, Aristotle and Jesus.
Non-scholarly literature, however, continued to rely on adaptation. France's Pléiade, England's Tudor poets, and the Elizabethan translators adapted themes by Horace, Ovid, Petrarchand modern Latin writers, forming a new poetic style on those models. The English poets and translators sought to supply a new public, created by the rise of a middle class and the development of printing, with works such as the original authors would have written, had they been writing in England in that day.
The Elizabethan period of translation saw considerable progress beyond mere paraphrase toward an ideal of stylistic equivalence, but even to the end of this period—which actually reached to the middle of the 17th century—there was no concern for verbal accuracy.
In the second half of the 17th century, the poet John Dryden sought to make Virgil speak "in words such as he would probably have written if he were living and an Englishman." Dryden, however, discerned no need to emulate the Roman poet's subtlety and concision. Similarly, Homer suffered from Alexander Pope's endeavor to reduce the Greek poet's "wild paradise" to order.
Throughout the 18th century, the watchword of translators was ease of reading. Whatever they did not understand in a text, or thought might bore readers, they omitted. They cheerfully assumed that their own style of expression was the best, and that texts should be made to conform to it in translation. For scholarship they cared no more than had their predecessors, and they did not shrink from making translations from translations in third languages, or from languages that they hardly knew, or—as in the case of James Macpherson's "translations" of Ossian—from texts that were actually of the "translator's" own composition.
The 19th century brought new standards of accuracy and style. In regard to accuracy, observes J.M. Cohen, the policy became "the text, the whole text, and nothing but the text," except for any bawdy passages and the addition of copious explanatory footnotes. In regard to style, the Victorians' aim, achieved through far-reaching metaphrase (literality) or pseudo-metaphrase, was to constantly remind readers that they were reading a foreign classic. An exception was the outstanding translation in this period, Edward FitzGerald's Rubaiyat of Omar Khayyam (1859), which achieved its Oriental flavor largely by using Persian names and discreet Biblical echoes and actually drew little of its material from the Persian original.
In advance of the 20th century, a new pattern was set in 1871 by Benjamin Jowett, who translated Plato into simple, straightforward language. Jowett's example was not followed, however, until well into the new century, when accuracy rather than style became the principal criterion.
Poetry presents special challenges to translators, given the importance of a text's formal aspects, in addition to its content. In his influential 1959 paper "On Linguistic Aspects of Translation," the Russian-born linguist and semiotician Roman Jakobson went so far as to declare that "poetry by definition [is] untranslatable."
In 1974 the American poet James Merrill wrote a poem, "Lost in Translation," which in part explores this idea. The question was also discussed in Douglas Hofstadter's 1997 book, Le Ton beau de Marot; he argues that a good translation of a poem must convey as much as possible not only of its literal meaning, but of its form and structure (meter, rhyme or alliteration scheme, etc.).
Translation of a text that is sung in vocal music for the purpose of singing in another language — sometimes called "singing translation" — is closely linked to translation of poetry because most vocal music, at least in the Western tradition, is set to verse, especially verse in regular patterns with rhyme. (Since the late 19th century, musical setting of prose and free verse has also been practiced in some art music, though popular music tends to remain conservative in its retention of stanzaic forms with or without refrains.) A rudimentary example of translating poetry for singing is church hymns, such as the German chorales translated into English by Catherine Winkworth. 
Translation of sung texts is generally much more restrictive than translation of poetry, because in the former there is little or no freedom to choose between a versified translation and a translation that dispenses with verse structure. One might modify or omit rhyme in a singing translation, but the assignment of syllables to specific notes in the original musical setting places great challenges on the translator. There is the option in prose sung texts, less so in verse, of adding or deleting a syllable here and there by subdividing or combining notes, respectively, but even with prose the process is almost like strict verse translation because of the need to stick as closely as possible to the original prosody of the sung melodic line.
Other considerations in writing a singing translation include repetition of words and phrases, the placement of rests and/or punctuation, the quality of vowels sung on high notes, and rhythmic features of the vocal line that may be more natural to the original language than to the target language. A sung translation may be considerably or completely different from the original, thus resulting in a contrafactum.
Translations of sung texts — whether of the above type meant to be sung or of a more or less literal type meant to be read — are also used as aids to audiences, singers and conductors, when a work is being sung in a language not known to them. The most familiar types are translations presented as subtitles projected during opera performances, those inserted into concert programs, and those that accompany commercial audio CDs of vocal music. In addition, professional and amateur singers often sing works in languages they do not know (or do not know well), and translations are then used to enable them to understand the meaning of the words they are singing.