Throughout the novel, The Strange Case of Dr Jekyll and Mr Hyde, Stevenson explores the idea of duality through both the characters and the setting of the novel. Specifically he explores the idea of duality within a person's personality, not only in Dr Jekyll and Mr Hyde but also Lanyon and Utterson. The use of Stevenson's descriptive language of the 19th century urban London, also demonstrates the idea of duality all around us. .
Primarily, Stevenson's examination of duality is shown through what appears to be the two characters of Dr Jekyll and Mr Hyde. It is demonstrated throughout the novel as the audience learns that these two distinct and apparently opposite personalities are in fact one person. Throughout Stevenson's novella, there are many descriptions of Mr Hyde which give an impression as to what he is like. Hyde is described as 'pale and dwarfish. He gave an impression of deformity' and 'Satan's signature upon a face'. The concept of duality is explored by the other personality of Dr Jekyll and his contrast to Mr Hyde in every aspect of his life. Dr Jekyll is a handsome man who is friendly and well liked. The fact that these two extremes of physical appearance and personality are in reality aspects of the same person explores the idea of duality. .
This aspect of duality is clearly demonstrated through Dr Jekyll's multiple appearances within the novella, however, Stevenson also examines the concept of duality in other characters such as Mr Utterson and Dr Lanyon. In the beginning of the novella, as Stevenson describes Utterson, it is shown that there are two sides to him. Conversely to Dr Jekyll and Mr Hyde, the idea that there are two sides to this man is shown through the contrasting aspects of his personality. Utterson is said to be a man who 'was never lighted by a smile', however, he is also described as 'somehow loveable' and that 'something eminently human beckoned from his eye'.