Comment critically .
“Logic” is a term tossed around a lot throughout the novel, but only Poirot uses pure, objective logic in his deductions. Most of the other characters who profess to use logic begin their explorations from a subjective or biased place, which ensures they will never arrive at the truth. Inspector Raglan, for example, assumes that the fingerprints he finds on the murder weapon must come from a stranger after he compares them to the fingerprints of everyone else in the house, but Poirot realizes that they could have come from Ackroyd himself. The inspector never would have considered this because it doesn’t appear to “make sense” or “be logical” when put in context of what he expects of a murder weapon. To Poirot, though, logic would dictate that if fingerprints are found, they be tested against everyone in the house, living or dead. By not allowing his preconceived notions to bias the steps he takes in his investigation, Poirot ensures that he can investigate with the purest logic, step by step.
