The simplest explanation is always the most likely

“The simplest explanation is always the most likely” is a principle Hercule Poirot states while correcting Arthur Hastings’s reading of the clues in the Styles case. It is not a command to accept the first plausible theory: Poirot’s method depends on examining details, distinguishing guesses from established facts, and abandoning an explanation when it fails to fit the evidence. The maxim’s force lies in its resistance both to imaginative overreach and to evidence arranged to look conclusive.

The Maxim and Its Method

Hastings admits that he drew erroneous conclusions from a few scribbled words. Poirot answers that imagination is useful only when kept in its proper place: it can assist inquiry, but it becomes a bad master when it outruns what the clues establish. The simplest explanation, in this sense, is the one that best accounts for the known facts, not merely the one that sounds most dramatic.

That distinction is visible in Poirot’s treatment of the despatch-case key. He says he did not know that it had been lost; he had made a guess. The twisted wire through the handle suggested that a key might have been wrenched from a flimsy ring, while the bright, evidently new duplicate on Mrs. Inglethorp’s bunch suggested that the original had been put into the lock by someone else. He presents the inference as a hypothesis built from particular observations, rather than disguising it as certainty.

Testing the Apparent Case

Poirot’s reasoning also resists a theory simply because it appears to fit a suspect. When Hastings treats Mr. Inglethorp’s absence as incriminating, Poirot calls it the point that tells against him: if he had known his wife would be poisoned that night, he would have arranged to be away from the house. His excuse for being absent may be false, but Poirot separates that suspicious circumstance from the distinct question of whether he knew about the murder. The unexplained absence leaves alternatives open; it does not, by itself, prove guilt.

The same discipline governs Poirot’s judgment of evidence that seems too complete. At Leastways Cottage, he argues that genuine evidence is often vague and unsatisfactory and must be sifted. The case against Mr. Inglethorp, by contrast, has been made so neat that its very conclusiveness is suspicious: in trying too hard to secure a conviction, the criminal has drawn the net so tightly that one cut can free the accused. Here the “simple” explanation is not the most immediately obvious accusation, but the account that explains why the accusation has been manufactured to look so decisive.

From the Coffee to the Medicine

The maxim reaches its fullest practical test in Poirot’s reconstruction of the poisoning. The initial contention is that Mrs. Inglethorp died of strychnine administered in her coffee, so Poirot asks when the coffee was served. Later evidence undermines that account: the coffee was not drunk, and the cocoa Mrs. Inglethorp heated and consumed contained no strychnine. The simplest explanation must therefore account for the poison without relying on either drink.

Poirot identifies the medicine as the missing medium. The strychnine was already present in Mrs. Inglethorp’s prescribed tonic; there was no need for the murderer to introduce it into the mixture. This explanation resolves the apparent contradiction between the untouched coffee, the harmless cocoa, and the fact that the fatal dose had been taken between seven and nine in the evening. Rather than add an unsupported step to the poisoning, it makes the existing medicine explain how the poison was taken.

Evidence, Timing, and the Final Link

The timing of the dose also matters. Poirot says the tragedy was intended for Monday evening: Mrs. Inglethorp’s bell wire had been cut that day, and Cynthia was staying with friends, leaving Mrs. Inglethorp isolated in the right wing. But she forgot her medicine while hurrying to a village entertainment, then lunched away from home the following day. The fatal dose was consequently taken twenty-four hours later than intended.

That delay gave Poirot the final proof. He produces three thin strips of paper and identifies them as a letter in the murderer’s own handwriting, addressed to Evelyn. The letter completes the chain of evidence that the earlier appearances had obscured. Across the investigation, the maxim thus links a modest intellectual caution—do not let imagination dominate—to a rigorous explanatory test: prefer the account that accommodates the concrete details, including the delays, objects, and contradictions, without mistaking a manufactured pattern for the truth.