“I rang the door-bell and was shown up to the chamber which had formerly been in part my own.

With hardly a word spoken, Sherlock Holmes waved me to an armchair. Then he stood before the fire and looked me over in his singular introspective fashion.

“Watson, you did not tell me that you intended to go into harness.”

“Then, how do you know?”

“I see it, I deduce it. How do I know that you have been getting yourself very wet lately, and that you have a most clumsy and careless servant girl?”

“My dear Holmes,” said I, “this is too much. It is true that I had a country walk on Thursday and came home in a dreadful mess, but as I have changed my clothes, I can’t imagine how you deduce it. As to Mary Jane, she is incorrigible, but there, again, I fail to see how you work it out.”

“It is simplicity itself,” said he; “my eyes tell me that on the inside of your left shoe, just where the firelight strikes it, the leather is scored by six almost parallel cuts. Obviously, they have been caused by someone who has very carelessly scared round the edges of the sole in order to remove crusted mud from it. Hence, you see, my double deduction that you had been out in vile weather, and that you had a particularly malignant boot-slitting specimen of the London slavey.”

In fiction, detectives like Holmes are usually portrayed as people with exceptionally brilliant minds. They possess the rare skill to see and analyze what ordinary people can’t. They have incredible abilities to infer, deduce, induce and conclude.

Then, there is G.K. Chesterton’s fictional catholic priest, Father Brown who relies on his extraordinary power of sympathy and empathy that enable him to imagine and feel as criminals do. He explains, “I had thought out exactly how a thing like that could be done, and in what style or state of mind a man could really do it. And when I was quite sure that I felt exactly like the murderer myself, of course I knew who he was.”

Sherlock finds the criminal by starting from the outside. He relies on science, experimental methods and deduction. On the contrary, Father Brown uses varied psychological experiences learned from those who make confessions of crime to him. He relies on introspection, intuition and empathy.

There is yet another set of detectives like those created by writers like Agatha Christie. Her Belgian detective, Hercule Poirot is a story-teller who draws information from the stories that others tell. He patiently listens to numerous accounts of what happened, where it happened and how it happened. He listens for credibility and ambiguity; he identifies why and how the pieces of the jig-saws don’t fit together. Ultimately, he uncovers the truth.

For the three detectives mentioned in the passage, which one of these would be non-essential for solving criminal cases?