By introducing dualism firstly in the setting, rather than the characters, give the reader an insight into the themes of concealment and secrecy that are present in the story. whilst also creating a sense of intrigue.
When first introduced to the elusive Mr Hyde, Mr Enfield is telling Mr Utterson about an incident he witnessed recently, where by Mr Hyde aggressively tramped over a young girl. It was hellish to see. It wasn't like a man; it was like some damned Juggernaut. The use of a simile to describe Mr Hyde conveys him as incredibly violent and uncaring. Like some damned Juggernaut connotes Mr Hydes animalistic behaviour and links to the idea of the best in man can be made. In Victorian times Darwins theory of the origin of the species (the theory that humans are descended from apes) wasn't accepted as many people believed it went against God. So therefore Stevenson making a reference to this when describing Mr Hyde connotes that his behaviour embodies this theory and he is behaving in a very animalistic nature. This is very contrasting to the ideas of Victorian morality as referring to someone as a juggernaut makes them appear to be very uncivilised and unpresentable.
Furthermore, when introduced to the character of Dr Jekyll, the idea of dualism is introduced between the two characters. Stevenson presents Jekyll as the pinnacle of respectability in chapter 3 the doctor gave one of his pleasant dinners to some five or six old cronies, all intelligent, reputable men as Dr Jekyll is linked with a group of well-regarded men, we are given the impression that the too is one of them. By referring to him as the doctor draws attention to his profession which would have been highly thought of in Victorian times, and again we are under the impression that Jekyll is a reputable and respected man, who embodies the ideas of Victorian morality. The contrast between the two men is evident, Dr Jekyll being well respected and esteemed, and Mr Hyde being aggressive and antagonistic.