The state of having two different or contradictory parts or aspects
Jekyll
His inner sinister desires and his outward respectable persona are in conflict with each other
This leads to his creation of Hyde
Hyde appears in the narrative before Jekyll
This reinforces the reader's perception that he is a separate entity rather than merely the alter-ego of Jekyll
Jekyll: 'Without Hyde, Jekyll lives a life of "profound duplicity"'
Jekyll
Presented as a respectable gentleman
Stevenson hints at his cunning, secretive and deceitful nature
Jekyll is not simply portrayed as a purely good character
This reinforces Stevenson's idea that human nature itself is both complex and multifaceted
Jekyll finds himself living a double life and he is unable to reconcile the two sides of his character
Jekyll wishes to be a respected doctor adhering to the highest moral standards
He also yearns to engage in malevolent acts
London
Stevenson presents the city with contrasting descriptions where affluent streets exist next to areas of degradation and poverty
Jekyll's house
The door at the front has a "great air of wealth and comfort" leading to the respectable Jekyll
The door at the back has an impression of "sordid negligence" leading to the repungant Hyde
The door is used as a metaphor for the inner struggles between their two identities
Stevenson uses this to comment on the deceptive outward appearance of upper Victorian society
Utterson
Described as a man having "a rugged countenance that was never lighted by a smile", but also a man of "soundness of mind and ease of manner"
Stevenson hints that Enfield has all the exterior of a gentleman, though may also have sinister secrets of his own
Jekyll: 'By the end of the novella, Jekyll acknowledges "the thorough and primitive duality of man"'
Stevenson continually uses contrasts to further underscore the aspect of duality throughout the novella: for example, rich/poor; light/dark; honesty/secrecy; night/day; inside/outside; respectability/notoriety
Stevenson is concerned about the duality of human nature and society in general and considers the idea that everyone is capable of good and evil deeds
Stevenson may also have used the dualities in the novella to reflect a society rapidly moving from the past into a new modern world