Jacobson and his concept of equivalence
He gave a new start to the theoretical analysis of translation since he introduced a new notion, which is equivalence in difference. He was an advocate of the semiotic approach to languages. On the basis of that approach he suggests 3 kinds of translation.
• Intralingual translation
• Interlingual translation
• Intersemiotic translation
Jacobson claims that in the case of intralingual translation the same language code is involved, though there’s no complete equivalence between an utterance and its transformation within the framework of the same language, because if we use synonyms or descriptive translation we cannot attain a one-to-one correspondence.
In case of interlingual translation the translator makes use of different codes and here can’t be full equivalence between language units of different codes, so translation here involves two equivalent messages in two different codes. He holds the opinion that from the point of view of grammatical structure languages may differ from one another to a greater or lesser degree, but a translation is still possible. So he acknowledges that the translator may face the problem of not finding a translation equivalent. Jacobson also acknowledges that when there is deficiency, terminology may be qualified and even amplified by low words and low translations and it may be amplified by neologisms and semantic shifts and finally by descriptions. So he compares the two languages: English and Russian, and comes to the conclusion that in case when there are no literal equivalent for a particular word or sentence, then It’s up to the translator to choose the most suitable way to render it to the TL text.

He stresses the fact that there are limitations of a translation when a linguistic approach is no longer suitable, when we can’t find an equivalent in a dictionary or a grammar book. Whenever a linguistic approach is not suitable, upon other procedures such as low translations, neologisms etc, both theories admit that a translation is always possible and the role of the translator who decides how to carry out the translation is great. So  his theory holds the view that translation is possible regardless of the cultural or grammatical differences between the SL and the TL texts.

Naida. Theory of formal correspondence and dynamic equivalence
Naida pointed out that there are two different types of equivalence naming formal equivalence, which is termed, as dynamic equivalence. Formal correspondence focuses on the message itself in both form and context. Unlike dynamic equivalence, which is based on the principle of equivalent effect, formal correspondence consists of a TL item, which represents the closest equivalent of a SL word or phrase. Naida makes it clear that here are not always formal equivalents between language pairs and suggests that these formal equivalents should be used wherever possible if the translation aims at achieving formal rather than dynamic equivalence. This can have serious implications, because the translator may not be easily understood. Naida admits that this formal correspondence distorts the grammatical and stylistic patterns of the TL and therefore distorts the message. In many cases misunderstanding is possible.
Dynamic equivalence is defined as a translation principle according to which a translator seeks to translate the meaning of the original text in such a way that the TL wording will trigger the same effect on the TL audience, which the SL text produces on the SL audience. The relationship is functional. Naida says that the form of the original changes, but the meaning remains similar. He introduces he principle of back transformation.
Naida has chosen the way of evaluative translation, because he was a famous translator of the Bible.