Nothing in human shape could have destroyed the fair child. _He_ was the murderer! I could not doubt it. The mere presence of the idea was an irresistible proof of the fact.
Chapter 7 · Narrator
Context
After glimpsing the creature in the storm, Victor instantly concludes it must be William's murderer. He bases this conviction not on evidence but on his certainty that no human could have committed the crime.
Analysis
Victor's logic spirals inward: "Nothing in human shape could have destroyed the fair child," so the non-human creature must be guilty—but this reasoning depends on the creature being categorically outside humanity. The phrase "the mere presence of the idea was an irresistible proof" admits that his conviction precedes evidence; the thought itself becomes its own justification, a circular logic that substitutes feeling for fact.
Essay Tip
Support a thesis that Victor's instant certainty reveals his need to externalize guilt—by declaring the creature non-human and therefore inevitably monstrous, he protects himself from recognizing his own responsibility for unleashing it.