With examples from Sesame Street, Wodehouse, Doctor Who, Sherlock Holmes and Star Trek. You can add your own duos too!

Watching “Star Trek into Darkness,” with the interactions between Zachary Quinto’s logical, calm, surpassingly knowledgeable Spock and Chris Pine’s intelligent, excitable, courageous, impulsive Kirk, on the heels of a healthy bout of P. G. Wodehouse’s “Jeeves and Wooster,” I was confirmed in my belief that every Famous Duo in literature and film can be explained and sorted on something I like to call the Buddy Spectrum.

What is the spectrum? It runs from order to chaos on one axis, and from total goofiness to extraordinary intelligence on the other. These divisions perhaps go back to Plato, with his notion of the two horses of the soul — thumos (courage) and passion (eros) tugging it in opposite directions, with the reason (logos) as the charioteer attempting to balance between them.

By moving along the two axes, you can describe pretty much every famous pair.  I was struck by the uncanny resemblance between Spock and the P. G. Wodehouse character Jeeves, the imperturbable, brilliant valet. Both convey a world of inflection in the infinitesimal tilt of an eyebrow, both are fonts of information, both provide the counterbalance to the impetuous swings of their more exuberant counterparts. Neither is the primary mover of his plot.

Duos with similar slopes on the graph have similar adventures.

Basically, the higher the combined total of their coordinates, the more adventure a given duo can compass. Sesame Street’s Bert (orderly) and Ernie (chaotic; see Order Muppets and Chaos Muppets, which more adequately describes the duo) don’t get out much. But Kirk and Spock can cover the whole universe.

There are two basic models within the system: the Complementary Duo (negative slope) and the Hero/Sidekick model (positive slope).

The Complementary Duo separates the impulse to adventure and the ability to resolve the adventure successfully into two persons. These are two people of whom, if they were ever separated, one would quickly veer off into chaos, and the other might stop moving altogether. How long they could survive on their own and how bad the eventual destruction would be varies. Leave Kirk to his own devices for a year and something may get blown up on a massive scale; then again, it may not. Leave P. G. Wodehouse’s lovable layabout Bertie Wooster to his own devices for a week, and he forgets how to dress himself or winds up married to some hideous prospect. Leave a Spock or a Jeeves to his own devices and nothing goes wrong, really, but nothing much happens.

The Hero/Sidekick model contains two people. One of them contains both the impulse to adventure and the ability to resolve the adventure successfully. Often, one critical moment establishes the necessity for the other party, but these moments do not occur in every case. The sidekick is either a Boswell-type narrator-biographer or simply a normal, if high-functioning, human being, who serves to point out the Hero’s dynamic qualities and ground him. You can tell which kind of duo you have on hand because it is possible to replace only one member of the duo and still go on adventures.

In most detective stories, the famous detective encompasses both the impulse and the resolution, and the sidekick merely narrates and offers backup. Agatha Christie’s Poirot, for instance, is the dynamic and the resolving party, and Captain Hastings merely goes along to narrate and offer occasional backup. House and Wilson, The Mentalist and Lisbon — scroll through a TV guide, and you will find a plethora of examples.

It is also possible to resolve these impulses into three or more people. In the Harry-Ron-Hermione triad, Harry contains the impulse to adventure, Ron has the loyalty and pluck, and Hermione has the intellectual firepower.

You can shuffle most famous duos in literature and film, the ones knotted with the stout cord of an ampersand, as Michael Chabon wrote, onto some part of the Buddy spectrum. It will tell you exactly how much adventure your duo can have and what shape that adventure will take (similar slopes have similar escapades — negative slope, the Jeeves or Spock has to rescue the Bertie or Kirk from a stew the latter has concocted; positive slope, the Sherlock or Doctor will fix whatever the preexisting problem is with the occasional aid of his companion or Watson).

I am not sure what practical applications this theory has, if any, or if someone else has hit on it previously, but for what it’s worth, there it is. You can argue with me about the additional notations. Map onto it what you choose.

Alexandra Petri writes the ComPost blog, offering a lighter take on the news and opinions of the day.