The grand thing is to be able to reason backwards.

A man with so large a brain must have something in it.

Detection is, or ought to be, an exact science and should be treated in the same cold and unemotional manner. You have attempted to tinge it with romanticism, which produces much the same effect as if you worked a love-story ... Some facts should be suppressed, or, at least, a just sense of proportion should be observed in treating them. The only point in the case which deserved mention was the curious analytical reasoning from effects to causes, by which I succeeded in unravelling it.'' —Sherlock Holmes on John Watson's "pamphlet", "A Study in Scarlet".

Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.

It's a wicked world, and when a clever man turns his brain to crime it is the worst of all.

Streams may spring from one source, and yet some be clear and some be foul.

I can never bring you to realize the importance of sleeves, the suggestiveness of thumb-nails, or the great issues that may hang from a boot-lace.