In literature, a symbol puts or draws together a specific thing with ideas, values, and attitudes towards persons or ways of life. It is usually a person, place, thing, situation, action, or the normal level of reality within a story. Allegorical symbols usually express a neater equivalence with what they stand for than the symbols found in modern realistic fiction (Gong, Kong 31). There is often an integral relationship between the symbol and the things it represents. It may have more complex and profound meanings beyond itself. Symbols range from the most obvious and mechanical substitution of one thing to another, such as, the blood image in Macbeth, or creations which are massive and perplexing, such as the white whale in Herman Melville’s Moby Dick. 
As for the symbolism, it has an extremely wide meaning. Sometimes it is used to describe certain mode of expression, which may refer to other things indirectly through the description of something else. In literature, symbolism can be defined as the artistic adoption of expressing certain emotion or ideas instead of describing then directly. It is not defining them through massive comparisons with concrete images. It suggests what these ideas or emotions are by recreating them in the reader’s mind through the application of unexplained symbol. This is only one aspect of the symbolism; there is also the other aspect, which is described as “transcendental symbolism” in which concrete images are used as symbols.
The utilization of the symbolism can make the article full of profound meanings. As a significant and famous writer in American Renaissance, Nathaniel Hawthorn is a great master of symbolism and allegory. The Scarlet Letter is one of Hawthorn’s most remarkable masterpieces, which also made Hawthorn well-known in the world. He adopted the symbolism so adeptly and skillfully in that it won him a great reputation.
Many American literature critics once claimed that Nathaniel Hawthorne is the pioneer who used symbolism in American literature. His writing skill has influenced so many writers. The Scarlet Letter is often seen as the first symbolic novel in American literature because Hawthorn uses symbolism skillfully and intelligently in this novel. D.H. Laurence said, that blue eyed darling Nathaniel knew disagreeable things in his inner soul. He was careful to send them out in disguise (Zhu 294). By analyzing symbolism in the work, we can have a keen insight into an outcast and a harsh society and the conflict of beliefs, thought and lifestyle, female emancipation, the essence of Puritanism and the conflicts of psychological independence in the middle of the seventeenth century.

II. The Changes of the Symbolic Meaning of the Letter A 

Every element of the novel is carefully conceived. Atmosphere, setting, characters and symbolism all mesh together to create a work of breathtaking power (Otfinoski, Steven 35-47).
The scarlet letter A has its different meanings with the evolvement of the story plot. These changes can be regarded as the clues running through this novel. They reflect not only the psychological growth in the characters, but also the attitudes of the people of the community in which they live. At first, the letter A is seen as a shameful symbol of sin and adultery. Gradually it becomes a symbol of alienation and loneliness, and then it is regarded as the representation of ability, angel and admiration.
2.1 The Adultery Between Hester Prynne and Arthur Dimmesdale
Henry James once said, In The Scarlet Letter, there is a great deal of symbolism; there is, I think, too much. It is overdone at times, and becomes mechanical; it ceases to be impressive, and grazes triviality (77-78). The most obvious symbolism in this novel is the letter A which symbolizes the adulterous relationship between Hester Prynne and Arthur Dimmesdale.
Because Puritanism has been widespread across the nation and has deep influences in American life, people tend to firmly stand for the importance of moral earnestness (Chadwick 27). The adultery arouses great discussion among people. It is not strange that people will laugh at Hester and think she is a woman without chaste. The scarlet letter A, which is worn on Hester's bosom, is firstly a shameful symbol of her sin and adultery against a handsome minister, Roger Chillingworth. At the beginning of the novel, many women stand in front of the prison door and regard wearing a scarlet letter A, which means Adultery, as a shameful sign for a woman. Because wearing a letter A in front of the bosom of the adulterous one is mental punishment in a puritan way to treat one as a criminal or the evil of adultery.  英文论文《红字》的象征意义(3):http://www.youerw.com/yingyu/lunwen_18617.html