Sherlock Holmes

"I have already explained to you that what is out of the
common is usually a guide rather than a hindrance.
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."

-- Sherlock Holmes in A Study In Scarlet: Chapter VII Conclusion

Sherlock Holmes

Sherlock Holmes closed his eyes and placed his elbows upon the arms of his chair, with his finger-tips together. “The ideal reasoner,” he remarked, “would, when he had once been shown a single fact in all its bearings, deduce from it not only all the chain of events which led up to it but also all the results which would follow from it. As Cuvier could correctly describe a whole animal by the contemplation of a single bone, so the observer who has thoroughly understood one link in a series of incidents should be able to accurately state all the other ones, both before and after. We have not yet grasped the results which the reason alone can attain to. Problems may be solved in the study which have baffled all those who have sought a solution by the aid of their senses. To carry the art, however, to its highest pitch, it is necessary that the reasoner should be able to utilise all the facts which have come to his knowledge; and this in itself implies, as you will readily see, a possession of all knowledge, which, even in these days of free education and encyclopaedias, is a somewhat rare accomplishment. It is not so impossible, however, that a man should possess all knowledge which is likely to be useful to him in his work, and this I have endeavoured in my case to do. If I remember rightly, you on one occasion, in the early days of our friendship, defined my limits in a very precise fashion.”

-- The Adventures of Sherlock Holmes: The Five Orange Pips