This article starts with the pure feature of language namely arbitrariness. Later on, he puts his finger on the existing differences among languages. finally, in the first part, the last mentioned point is the ability of language to express ideas and thoughts. At the beginning of the second part, translation was described as the conveying the intended message through SL and TL. Then, the translation was considered as the sub field of applied linguistics. Having used the contrastive analysis, the writer attempted to define equivalence by considering the translation as the process of both encoding and decoding. The writer, later on, exemplified between Persian and English languages to illustrate the concept of equivalence. To this end, the writer provides some examples regarding cultural words, verbs, polysemy, compound adjective, implicitness, explicitness, prepositions, literary terms, simple words, compound words, genitive case, future tense, passive structures, theme, and rheme. As it is seem here, the writer aimed at applying different structures in order to indicate the fact that language systems vary and the translation involves knowing these differences.

To put it in a nutshell, in order to translate correctly and accurately, the translator needs to know the phonological, morphological, syntactic, semantic, pragmatic, idiomatic and cultural systems of both source language and target language. After knowing this, the translator decodes the SL elements and encodes them in to TL elements. All in all, the main purpose of this article is to define and explain the concept of equivalence. In order to end the purpose, the writer went in to details by providing the readers with a number of examples cristalize the areas defined in the article. The writer, finally, reached the fact that if somebody or a translator wants to translate satisfactorily; s/he needs to be familiar with the linguistic system and cultural system of the source and target languages.