helps give it meaning by bringing it closer to similar
clues, and separating it from those dissimilar from it. In this way, there is a plurality of signs to be mobilized in every
interpretation of clues, and not, as one might think, one isolated sign.
If all deduction rests on knowledge and includes a share of comparison—allowing one to compare a given clue to other clues—it
also involves another operation, aimed this time at understanding how the clue came into being, reconstructing its evolution.
This second operation, which could also be called analysis, is described to Watson by Holmes in A Study in Scarlet as “reasoning backwards”:
“In solving a problem of this sort, the grand thing is to be able to reason backwards. That is a very useful accomplishment,
and a very easy one, but people do not practise it much. In the every-day affairs of life it is more useful to reason forwards,
and so the other comes to be neglected. There are fifty who can reason synthetically for one who can reason analytically.”
“I confess,” said I, “that I do not quite follow you.”
“I hardly expected that you would. Let me see if I can make it clearer. Most people, if you describe a train of events to
them, will tell you what the result would be. They can put those events together in their minds, and argue from them that
something will come to pass. There are few people, however, who, if you told them a result, would be able to evolve from their
own inner consciousness what the steps were which led up to that result. This power is what I mean when I talk of reasoning
backwards, or analytically.” 24
As in all of Holmes’s investigations, reasoning backward is omnipresent in The Hound of the Baskervilles ; it occurs during the reading of each clue. It is reasoning backward that allows Holmes to guess, for example, that the footprints
left on the yew alley changed shape because Sir Charles Baskerville had started running.
But beyond the isolated interpretation of each clue, reasoning backward is integral to Holmes’s larger attempts to suggest
an overall version of what happened. It is the association of the tanned face, the wounded left arm, and the military appearance
of a physician that leads Holmes to conclude that Watson has returned from Afghanistan. Similarly, it is the association of
a whole series of clues (Dr. Mortimer’s testimony about a dog’s footprints, Selden’s death, Laura Lyons’s testimony, Stapleton’s
resemblance to the Baskervilles, Beryl Stapleton’s testimony, and so on) that leads Holmes to his final hypothesis.
Thus, reasoning backward, closely linked with comparison, is the final, essential step in interpreting clues. Whereas comparison
opens up an initial, very general reading of the clue, reasoning backward refines this suggestion by reviewing the particular
way it was formed, thus yielding its true meaning.
The Holmes method, the one we see at work in the very first Holmes story and in all the cases that follow, rests on three
operations: observation, comparison, and reasoning backward.
As the detective indicates in his conversation with Watson, these three processes sometimes all occur at the same time (“From
long habit the train of thoughts ran so swiftly through my mind, that I arrived at the conclusion without being conscious
of intermediate steps. [ . . . ] The whole train of thought did not occupy a second.” 25 ). Nonetheless, it is desirable to separate the three constituent operations of Holmes’s method if one wants to study how
they function.
Thus presented, this method offers all the appearances of rigor, since it rests on logic and relies on the discoveries of
science. (We too will come to use it, especially when we resort to animal psychology and backward reasoning.) But can Holmes
be sure that his trusted method will lead him to the truth? Nothing could be less certain, as we shall see.
* Another form of
Elizabeth Amelia Barrington