Nec verbum verbo curabis reddere fidus interpres, Horace [As a true translator you will take care not to translate word for word]
Dictum non verbum de verbo, sed sensum exprimere de sensu, St. Jerome [Not a word-for-word translation, but a translation that should express the sense as derived from the general meaning]
This interesting post from a blog on wordpress explains the difference between “word for word” and “dynamic equivalence” and argues that a balanced approach employing both is the most desirable. I will quote some parts of it.
Translation of any language is very much like reading music. Instead of notes, you have letters. Instead of chords, you have words. Instead of phrases, you have clauses. Instead of periods, you have sentences. The parallels go all the way up. In music, there is meaning on each one of these levels.
(…) the best-articulated translation philosophy I have found out there is the preface to the Holman Christian Standard Bible. They opt for the “optimal equivalence,” a philosophy that exhaustively examines the text “at every level (word, phrase, clause, sentence, discourse) in the original language to determine its original meaning and intention.” Their practice is then to use literal whenever possible, but when clarity demands an idiomatic translation, they will go for that, and put the literal translation in the footnote.