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4. It was on the moral side, and in my own person, that 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; and from an early date . . . I had learned to dwell with pleasure, as a beloved daydream, on the thought of the separation of these elements.

This quotation appears midway through Chapter 10, “Henry Jekyll’s Full Statement of the Case," which consists of the letter that Jekyll leaves for Utterson. The letter allows us finally to glimpse the events of the novel from the inside. In this passage, Jekyll discusses the years leading up to his discovery of the potion that transforms him into Hyde. He summarizes his theory of humanity’s dual nature, which states that human beings are half virtuous and half criminal, half moral and half amoral. Jekyll’s goal in his experiments is to separate these two elements, creating a being of pure good and a being of pure evil. In this way he seeks to free his good side from dark urges while liberating his wicked side from the pangs of conscience. Ultimately, however, Jekyll succeeds only in separating out Hyde, his evil half, while he himself remains a mix of good and evil. And eventually, of course, Hyde begins to predominate, until Jekyll ceases to exist and only Hyde remains. This outcome suggests a possible fallacy in Jekyll’s original assumptions. Perhaps he did not possess an equally balanced good half and evil half, as he thought. The events of the novel imply that the dark side (Hyde) is far stronger than the rest of Jekyll—so strong that, once sent free, this side takes him over completely.