In his Decalogue (ten commandments) for detective fiction, Fr. Ronald Knox’s ninth commandment was:

The stupid friend of the detective, the Watson, must not conceal any thoughts which pass through his mind; his intelligence must be slightly, but very slightly, below that of the average reader.

The Watson in a detective story is generally understood to be a stand-in for the reader, and not without reason. I’ve been wondering how necessary a Watson character is, so I’d like to look at the functions of a Watson:

1. To have someone to whom the detective must explain this thinking and actions.
2. To have someone for the detective to talk to.
3. To have someone who looks up to the detective.

Regarding the first, it can be very helpful for the detective to need to explain himself. How the detective thinks is interesting and apart from having to explain himself we mostly won’t know. It is always possible to give him a habit of thinking out loud, of course; one sees this a bit with Chesterton’s Father Brown (who generally doesn’t have a Watson character).

Regarding the second, this is acknowledging the truth that it is not good for man to be alone. But the companion of a detective does not need to be a reader stand-in and often is better if he isn’t. My favorite example of this is Harriet Vane in the Lord Peter Wimsey mysteries. She’s not on Lord Peter’s level, but she’s also not—generally—a reader stand-in.

I should mention that Harriet Vane only appears in 4 of the Lord Peter books; Lord Peter’s companion is more often his friend, Charles Parker. Parker is more of the typical Watson character; I suppose my marked preference for Harriet Vane is sufficient to give my opinion of this.

Regarding the third quality of a Watson, this gets to a somewhat tricky aspect of art—most of conveying grandeur is done not by conveying it but by conveying how people react to it. Grandeur is a very difficult thing to show; people being impressed is much easier to show. Perhaps one of the best examples of this is the line, supposedly said by Katherine Hepburn, describing Fred Astair and Ginger Rogers, “He gave her class and she gave him sex [appeal]”. It’s true, though not literally so.

Fred Astair had sex appeal, but Ginger Rogers (in how she acted her roles, I mean) recognized it and made it intelligible; she reacted to him as if he had sex appeal, making it clear he did. Ginger Rogers had class, but Fred Astair (again, in how he acted in his roles) treated her as if she was classy, making it clear to the audience that she was. Much of either—how we in the audience know them—is by the reactions to them.

And so it is with the brilliance of the detective. The detective must actually be brilliant or the Watson will only come off as a farce. But if the detective is brilliant, the Watson failing to understand and being enlightened will show the detective’s brilliance off.

Now, when it comes to how necessary these are, I think that the second—companionship—works fairly well, if not better, with an equal. The first and third do require someone who is not an equal, but they don’t need to be an associate of the detective. There will always be bystanders present who can take an interest in what the detective does, and he will suffice to ask questions and be impressed. There is even a potential benefit to this approach in that Watson might be a one-off, but if the detective is constantly running into people who are impressed with him, it lends credence that this is the normal reaction to him.

Of course, the two can be mixed; third parties can relieve the Watson of his duties on occasion in order to spread the work around.

I don’t really have a conclusion, here, other than to say that I don’t think that a Watson is strictly necessary. They’re a good option, but not, I think, a requirement.