Holmes is able to utilise logic and establish the true sequence of events by eliminating extraneous information. In ‘The Speckled Band’ he works out that the band has nothing to do with a troupe of gypsies – the red herring in the story – but a venomous snake. Holmes investigates each area of Miss Stoner’s room and clarifies his assumptions once Mr Roylott has been made victim of his own evil scheme-
My attention was speedily drawn, as I have already remarked to you, to this ventilator, and to the bell-rope which hung down to the bed. The discovery that this was a dummy, and that the bed was clamped to the floor, instantly gave rise to the suspicion that the rope was there as a bridge for something passing through the hole and coming to the bed. The idea of a snake instantly occurred to me, and when I coupled it with my knowledge that the doctor was furnished with a supply of creatures from India, I felt that I was probably on the right track.
In ‘The Advantage of the Blue Carbuncle’, Holmes’ examination of the hat belonging to the man with the goose reveals an in-depth understanding of the man’s physical, mental and social condition-
“pray tell me what it is that you can infer from this hat?”
He picked it up and gazed at it in the peculiar introspective fashion which was characteristic of him. “It is perhaps less suggestive than it might have been,” he remarked …That the man was highly intellectual …he was fairly well-to-do within the last three years, although he has now fallen upon evil days. He had foresight, but has less now than formerly…which, seems to indicate some evil influence, probably drink, at work upon him... These are the more patent facts which are to be deduced from his hat.
Holmes reviews Watson’s earlier perceptions of his skill in ‘The Five Orange Pips’ -
Philosophy, astronomy, and politics were marked at zero, I remember. Botany variable, geology profound as regards the mud-stains from any region within fifty miles of town, chemistry eccentric, anatomy unsystematic, sensational literature and crime records unique, violin-player, boxer, swordsman, lawyer, and self-poisoner by cocaine and tobacco. Those, I think, were the main points of my analysis.
Holmes asserts that it is the ability to hone and apply this diverse knowledge in a logical way that is the root of his genius.