I'm going to assume that most people reading this are familiar with the concept of 'Chekhov's gun', but just in case, it's the principle that every memorable element of a story should serve some sort of purpose. If there's no purpose, if there's no pay-off, the offending element should be removed.

Anton Chekhov explained it much better than anyone else could.

"Remove everything that has no relevance to the story," he once said. "If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off. It it's not going to be fired, it shouldn't be hanging there."

In a letter to fellow playwright Aleksandr Semenovich Lazarev, he explained it even more succinctly: "One must never place a loaded rifle on the stage if it isn't going to go off. It's wrong to make promises you don't mean to keep."

Has there ever been a weapon more memorable — and ultimately useless — than Luke's lightsaber in A New Hope?

(Incidentally, I know some fans hate referring to the original Star Wars as A New Hope, a subtitle that was tacked on after its release. I'm going to use it here to differentiate it from the other films in the saga, but trust me — I know it's really called Star Wars, you know it's really called Star Wars, we all know it's really called Star Wars.)

Think back to the scene when Luke gets his lightsaber. It's a big deal, and clearly foreshadows that this thing is going to play a key role in the story.

"Your father's lightsaber. This is the weapon of a Jedi Knight," Obi-Wan tells our intrepid young farm boy. "Not as clumsy or random as a blaster. An elegant weapon, for a more civilised age."

I mean, come on — if those Tatooine nights ever got cool enough to justify Obi-Wan installing a fireplace, he would have had that lightsaber hanging right above it.

Sure, Obi-Wan uses his lightsaber in the second act, but his isn't the one that was introduced with such fanfare. And Luke trains with his aboard the Milllenium Falcon — but that's not delivering on the promise of the lightsaber's introduction; that's just further build-up to a pay-off that never comes.

The training sequence actually compounds the structural problem we've got here, because the prominence of the lightsaber, and the difficulty Luke has wielding it, really sets up the expectation that Luke will need to prove his mastery with the laser blade to succeed.

To put it in terms Joseph Campbell would appreciate, the lightsaber is Luke's amulet, the magical item given to him by a wise elder that he must use to complete his hero's journey. When people compare Star Wars to the legend of King Arthur, it's because Luke Skywalker is running around with a goddamn sword of destiny.

Instead, Luke establishes himself as a hero by blowing up the Death Star with a proton torpedo. He uses The Force to do so, sure, but at no stage of the film is he required to even switch his lightsaber on in a combat situation.

Yes, Luke uses his lightsaber to great effect in the sequels, and if you want to view A New Hope as the first act in a three-act structure, that's fine. But it's not how the film was intended to be viewed when it was released, and it's incompatible with the idea that the original Star Wars works perfectly as a stand-alone story.

The Death Star trench run is one of the most thrilling finales in the history of cinema. It's so good, in fact, that it helped everyone ignore the fact that the plot of Star Wars doesn't deliver on its promises.

Obviously, things worked out pretty well for the film the way it was, but it still seems like Luke should have been required to use his lightsaber in some instrumental way in A New Hope.

At one stage, at least, George Lucas agreed.

"Between the second and third drafts, Luke stopped on the surface of the Death Star," Lucas revealed in an interview included in JW Rinzler's essential tome, The Making of Star Wars.

"He and Artoo had to take the bomb by hand, open up the little hatch, and drop the bomb in it — then they had fifteen seconds or something to get off the surface before the thing blew up — but as they were going back to the ship, Darth Vader arrived.

"So Luke and Vader had a big swordfight. Luke finally overcame Vader and then jumped in the ship and took off."

Of all the treatments and drafts Lucas produced of the Star Wars script befofe he began filming, the only one that Luke and Vader's swordfight can be found in is a six-page synopsis Lucas wrote in 1975 to help Fox executives get their heads around his weird little space movie.

I think this synopsis is where Star Wars really became, well, Star Wars; where it really came into focus as a fairy tale that just happened to be set in space. It was around this stage of the process that Lucas says he spent a year reading fairy tales, and Joseph Campbell's The Hero With a Thousand Faces, and started to make a conscious effort to make his story fit that classic mold.

This synopsis is where Obi-Wan Kenobi — at this stage just an unnamed wizard who literally appears on the side of the road — first appears in Lucas' writings, and where the princess first needs rescuing. Luke's swordfight with Vader is a perfect fit with the type of story Lucas now knew he was telling.

So, why didn't it happen?

Before he wrote the next draft, Lucas decided that the swordfight might undercut the momentum of the film, and he cut it out completely.

"In trying to intercut the dogfight with the old-fashioned swordfight," he's quoted as saying in The Making of Star Wars, "I realised that the film would have just stopped dead. It's too risky."

Lucas never came close to actually filming the battle between Luke Skywalker and Darth Vader on the Death Star's surface, but it seemed like such an obvious conclusion to the story that artist Howard Chaykin used it on the cover for the sixth issue of Marvel's Star Wars comic book adaptation.