In his novel, The strange case of Dr Jekyll and Mr Hyde, Robert Louis Stevenson explores the duality of human nature - that man is, at once, both evil and good. In his characterization of Mr Hyde as Dr Jekyll's evil persona, he wishes to convey the intricate complexity faced by man: "What is my true nature, my true will? To exercise goodness and humility or to succumb to savage desire and degradation?"
Robert Louis Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde depicts a man torn between his "good" and "evil" self. This idea has been popularized in Gothic Romantic works (like Stevenson's text and Mary Shelley's Frankenstein). Gothic Romantic authors, when dealing with the doppelganger (a person's "twin"), play upon the idea that people possess both good and evil within themselves. While the amount of good and evil is unknown, everyone possesses the ability to be both good and evil.
A thesis statement which addresses the idea of good and evil within the text is as follows.
The dual nature of human mentality, symbolized by the evil of Mr. Hyde and the good of Dr. Jekyll, illustrates the battle which rages within an individual. Robert Lewis Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde represents the battle between the intellectual and rational self and the irrational and animalistic self.
A good thesis statement about good and evil from The Strange Case of Dr. Jekyll and Mr. Hyde is that good and evil are not distinct from each other but are intertwined and defined by each other. Dr. Jekyll, the quintessentially morally upright man in the eyes of society, has long contended with the secret darker side of himself. He writes a letter in which he explains his understanding of the dualistic nature of humans:
I learned to recognise the thorough and primitive duality of man; I saw that, of the two natures that contended in the field of my consciousness, even if I could rightly be said to be either, it was only because I was radically both.
In other words, he realizes that he can only be good and upright because he also has a darker and more evil side to himself. He also realizes that all of humankind also has this duality and that good can only exist alongside evil because it is defined by its opposite.
When Dr. Jekyll tries to use a drug to separate his evil side, Mr. Hyde, from his good side, he finds this situation untenable. The evil actions Mr. Hyde has carried out make Dr. Jekyll so repulsed that he winds up killing himself. Dr. Jekyll recognizes that good and evil must exist alongside each other and temper each other and that they cannot exist ever as unadulterated good or unadulterated evil. It is instead our internal battle between good and evil that defines us as human beings.