"man is not truly one, but truly two"
Jekyll, Chapter 10: Henry Jekyll's Full Statement of the Case
A starting point
"This shows duality because Jekyll has two sides to his personality."
Develop the analysis
The contrast between "one" and "two" challenges the idea of a single, consistent identity. Jekyll's use of "man" extends his claim beyond himself, presenting divided desires as part of human nature. Yet his attempt to separate those desires leads to disaster, suggesting that recognising inner conflict does not free him from responsibility for his actions.
An illustrative analysis, rather than a graded model answer. Link your interpretation to the specific essay question.