Robert Louis Stevenson was born in Edinburgh， Scotland （1850-1894）. He was a novelist， a poet， and a travel writer. He was also on behalf of new romanticism in English literature. Stevenson was one of the most prolific writers. His representative novels were Treasure Island， Dr. Jekyll and Mr. Hyde and so on. He traveled a lot when he was young. The experience of his traveling accumulated rich resources for his writing. The novel Treasure Island （1883） was his masterpiece. It was a story about finding the buried treasure. It was the most popular one among his romantic novels. It was also the most popular English reading material for children. Dr. Jekyll and Mr. Hyde was a satire work about dual personality. At the same time， it was a novel about the description of suspenseful thrillers. His prose， travel notes and letters were beautiful in writing. The resource of the content was very rich. Stevensons work was so popular that he was praised by many writers including Ernest Hemingway， Jorge Hector and other famous writers. But when he died， his reputation in literary began to decline. The latter generation only thought that he was an outstanding childrens story writer. Many modern socialist writers didnt accept him， because although Stevenson was popular， his work was not accord with their definition of the literature. However， in the middle of the twentieth century， the reviewer reassessed the works of Robert Louis Stevenson. They started to admire Stevenson and listed his works to the classic works of the west and regarded him as one of the greatest writers in 20 century.

Dr. Jekyll and Mr. Hyde is one of the most famous works of Robert Louis Stevenson. After publication since 1886， it was adapted into plays and films， and fashionable all over the world. The work discussed an eternal theme which existed in our daily life—dual personality. Dr. Jekyll was a respectable gentleman who always did charity and made contributions to the society， but in his inner world， he wanted to pursue pleasure and did some evil things. If so， he would lose the ideal image among the public， so he wanted to invent a kind of chemical potion to split the bad aspect from the good one. Fortunately， his experiment succeeded. At day time， he was Dr. Jekyll who threw himself into science research. At night， he drunk the potion and became Mr. Hyde， who had a very different face. He did many evil things， but nobody knew that actually he was Dr. Jekyll. After that， Dr. Jekyll showed great fear. Gradually， Dr. Jekyll felt that Mr. Hyde was so strong that he couldnt control. Finally， he killed himself， at the same time， killed Mr. Hyde. This work tells us that people should control the evil aspect and develop the good aspect to make contributions to our society.

Dual personality is a very rare and incurable mental illness. So far we have found not more than 1000 people who have dual personality， and the people who have more than two personalities are not above 50. （http：//wap baike.Baidu.com） But there are a lot of people who like to take dual personality to flaunt themselves. In fact， this is not scientific. Dual personality is one kind of multiple personality， which is a serious psychological barrier. We can explain dual personality like this：A man with two relatively unique but mutually separated personalities. It is a kind of mental illness that can bring many troubles for him. The basic characteristics of dual or more personality is， although the same individual has two or more different personalities， but in a time， only one side is obvious. Each character is complete， and has its own memory， behavior and preference. Multiple personality can be dual， triple， or four personalities..... So far， the most can achieve 24 personalities. （http：//wap baike.Baidu.com） Among them， dual personality is the most common one. Usually one of the sides is the dominance and it is hardly aware of the existence of the opposite side. The two sides cannot linger in memory at the same time. When he wants to do bad things or pursue pleasure， he shows us the evil aspect. But when he is relaxed or satisfied， he shows us the good aspect. Dual personality is a kind of illness， so it is indispensable to turn to doctor. Keeping a relaxed mood and making contact with others are very useful way to keep away from dual personality.

Dr. Jekyll and Mr. Hyde is a bright pearl in the literary world which means dual personality. So Jekyll and Hyde also become the commonly used words. But there are only a few readers study this short story in domestic learning sphere. The readers analyze this novel in many different perspectives. Xie Zhilong combines dual personality with the original sin in The Unity of the Good and Evil in Dr. Jekyll and Mr. Hyde. （Xie Zhilong， 2011：136） He thinks that people are born with sin， so the original sin makes it difficult to control the evil desire. Some readers use id， ego， and super-ego to describe the implicit self and actual self， such as Wang Yanhui in Analysis of Personal Split in ‘Dr. Jekyll and Mr. Hyde with the Theory of Fred Sigmund. Implicit self like id， it is the original desire for human beings， no matter it is right or wrong. And the actual self like super-ego. When the desire is evil， it can control itself to develop towards the good direction. Yu Xinhong compares Dr. Jekyll and Mr. Hyde with The Picture of Dorian Gray in Person and Shadow—A Comparative Analysis of ‘The Strange Case of Dr. Jekyll and Mr. Hyde and ‘The Picture of Dorian Gray. （Yu Xinhong， 2010：1-59） He compares the persona and shadow in the two novels. He makes a conclusion：Everybody should confront his own shadow. It should be known to all， to become responsible for ones own shadow is to make ones morality less compulsive and less blind. Inspired by his viewpoints， I intended to analyze the dual personality in Dr. Jekyll and Mr. Hyde. Seeing the world of human beings， we can find the good and evil of personality everywhere. So it is significant to keep balanced between the good and evil not only for personal development， but also for social harmony.

Dr. Jekyll and Mr. Hyde is known for its lively description of dual personality. This short story is different from others， because both good and evil in this novella exist within one person. Actually， in daily life， good aspect and bad aspect coexist with one person. This provide possibility for dual personality. That is to say， Dr. Jekyll and Mr. Hyde can exchange with each other.

In the novella， Dr. Jekyll comes out as a person who is a wealthy doctor with so much respect in London. He is a tall， well-made man with a kindly face. Whereas Mr. Hyde is a small， short and strange-looking man who is hated by the people all over London. There is something wrong with his appearance， something ugly and unpleasing. He is happy to do bad things. When we analyze those two characters， we split a complete person into the extreme good and extreme bad. There is no coordination between them. Although it is a bit exaggerative， it is the true features of personality. Dr. Jekyll was a gentleman and he made great contributions to science. He always did charity， but it is from such a person that split a greedy， ugly， disgusting criminal. Although Dr. Jekyll knew that the evil was taking over the good， but he didnt resist the temptation to become an evil to break the law and commit crimes. Finally， he was destroyed between happiness and reality. Dr. Jekyll wrote in his confession：

The good and evil coexist within one person， so Dr. Jekyll cannot control himself to become Mr. Hyde. Imagining that one person only has the good aspects or the bad aspects， it is impossible for him to hold dual personality. So it provides possibility for Dr. Jekyll to become Mr. Hyde.

As we all know， the people who makes great effort to pursue reputation and keeps the ideal image in the mind of the public may have some problems in his mind. In the novella， Jekyll is a doctor who has status in society. Everyone respects him. He is a quite cultivated man who always does charities. Dr. Jekyll stands high in the public estimation. By wearing this persona， Dr. Jekyll restricts himself to a form which he hopes to receive acceptance from the public. This kind of acceptance makes the social communication much easier， just like the beautiful clothes make a person more pleasing. Enjoying the high reputation as a gentleman and engaging in charity work， Dr. Jekyll stands for moral and upright. Dr. Jekylls reputation plays an important role in the split of his personality. When he was on public occasion， he spared no efforts to keep the respectable image in the publics mind. When he was along， he was wild， fun-loving， and irresponsible. He did bad things everywhere. People all over London regarded Dr. Jekyll as a serious， successful gentleman. They thought highly of him and respected him as their superstar. With this great pressure， Dr. Jekyll pretended to be a gentleman in pubic place to keep the ideal image in the mind of the public. He thought that jokes were a contradiction to his respectable reputation.

By thinking so， the balance between his good aspect and bad aspect is broken， so he wants to separate the good side and the dark side from each other.

At last， Dr. Jekyll succeeded to invent a kind of potion with the right mixture of chemicals. By drinking this potion， he could become Mr. Hyde， who was a complete villain. Dr. Jekylls success proved that he was an excellent doctor and he was more capable than Dr. Lanyon in medical fields.

Dr. Jekyll was a medical doctor over 50 years old or so， He was born with a lot of heritage， and extraordinary talent. When he grew up， he had a successful career， and his manner was humble. He received respect and love from the people around him. But in his inner world， a desire to pursue pleasure always turned up. Whereas his family and family background did not allow him to whatever he wanted. So on the one hand， he did bad things privately. He held up his head high and advanced by long strides. He also took a decent and serious looks. When he grew up， it was discovered that he had a dual personality in life. When the conflicts between the constrained desire and the real life emerged， he did not want to give up his desires. On the contrary， he thought that he found the truth of the human nature：“The good and evil coexist in human beings”. Hence he imagined to separate the good and evil from mans nature by experiment. As a medical doctor， Jekyll was fascinated by how to separate the good and evil through chemical medicament. He hesitated for a long time between the starting of his vicious desire and putting it into practice.

【作者簡介】張鑫，蘭州交通大學。