involves the relation between the source text and the target text, it limits the range of justifiable target-text functions for one particular source text and raises the need for a negotiation of the translation assignment between translators and their clients.”; Third, the function of a translation work should be taken into account. “Function” indicates the factors that gurantee the target text working in a intended way in the target situation, it mainly involves four aspeacts: referential function, expressive function, appellative function and phatic function, they jointly affects specific problems and solutions in translation.

Nord has made great contributions to the development of translation theory, but in the practice of translation, it is difficult to keep balance among the client, the writer and the readers. How to solve the disputes when the purpose of the source text is contradict with that of the target text is a tough work, and we still have to explore efficient solutions in the process of translation.

3. On Subtitling
3.1. The Characteristics of Subtitling
(1)Colloquialism
TV series or films mostly are dialogues and daily talks, apart from some special situations requiring official or standard language, most contents are colloquial. This characteristics determines that when we are translating, we must pay more attention to the oral or slang language, such a “john” “third wheel” “let the cat out of the bag” and so on.

(3)    Entertainment and Fashion
Now computers are available to most people, and the popular words on the Internet  
also affect people’s daily life, such as E-mail,otaku .etc. More and more person tend to accept web culture for they like to watch TV shows and films on the Internet. Web culture is somehow a fast-food culture. It changes and disappears quikly. The words of different countries are imitating and permeating each other.

(3)Association
Subtitling links with the picture, the voice and the music .etc of a work, it can’t exist alone. If we want to understand the true meaning of a foreign TV show or a film, we must know all aspects of it, and mere subtitling is not enough. The meaning of literature work can be made up by our imagination when we read the words, but if we just refered to subtitling on TV, we would have misunderstanding and doubts.

3.2. The restrictions of Subtitling
(1)Time limitation
Subtitling requires that the words should synchrionize with the picture. As the actors speak fast and end in a few seconds, the audience must understand the given subtitle in a very short time to follow up the pace, then translators must use simple and vulgarized language to interpret them, such as using short sentence to replace long sentence or changing a passive sentence into an active sentence.

(2)Space limitation
Subtitle always appear on the bottom in a frame,generally, the words is less than 30 units. Too many words will affect the aesthetic property of a picture so as to distract the audience’s attention. To reach the purpose of communicating,translators must controll the numbers of words in a concise and straightforward manner.
(3) Culture limitation
 
Translation is not just a process of converting language, what’s more important is making up cultural differences. Because of the existence of culture limitation, translators must consider how to obtain the source-text cultural characteristics on the one hand,and to blend into the target-text culture so as to make the audience accept it easier on the other hand.

3.3. The Strategies of Subtitling
Li Yunxing generalized the main strategies of subtitling into three principles：deduction, simplicity and straightness. Good translation is the combination and flexible conversion of them.
(1)    Deduction
“deduction” involves three ways: condensation,reductive paraphrasing and deletion.“condensation”means only translate the essential or central part of the source text;“reductive paraphrasing”asks for a short or simple sentence to express the meaning of the original work; “deletion”means all parts are omitted. The operating principle of deduction is “relevance ” which means unrelated factors can be deleted or condensated to highlight the relevant imformation condusiving to the cognitive activities. 从《生活大爆炸》看美剧字幕翻译的文化转向(4):http://www.youerw.com/yingyu/lunwen_2419.html