"If you have it, you've gotta use it."

Primer (2004) is a complex and challenging film. This article is intended to help you get the most enjoyment out of watching it.

Update: I've recorded a commentary track for the film. It covers most of what's explained below, but has some new stuff too!

What should I know before watching Primer?

(If you want to go in totally blind, that's fine - skip the rest of this section.)

Primer has nothing that could be termed exposition. Nothing will be explained to you directly; you are essentially eavesdropping on other people's conversations as you follow them around. It's up to you to keep up. Consider turning on the subtitles. Some of the dialogue is muffled or occurs in the background where it's harder to catch. Even if you're firing on all cylinders, there's a point about 3/4 of the way through the film where everybody - everybody - loses it on the first watch. This is not your fault; this part of the film is very confusing and not explained very clearly. I will explain it later.

Now go watch the film and then come back.

Here is a summary of what literally takes place in the film.

Aaron, Abe, Philip and Robert are four men who work at a semiconductor firm by day and sell home-made electronic products in their spare time. But while they've had some interesting patents, they haven't made major money from the side projects. They came close once, but a man named Joseph Platts stole their idea, leaving them with no recourse.

It's been agreed that they each take turns to put an idea forward. Robert's idea is to build a strange piece of hardware which can theoretically reduce the mass of an object inside it. It does this by "blocking information", cutting the object in the box off from the effects of gravity. This is just after Christmas time (hence Aaron's new refrigerator).

The box requires superconductivity. They can't generate the low temperatures they need, so in the brainstorm session they throw out an idea or two for doing it at room temperature. They cannibalise some home appliances for equipment and a catalytic converter for palladium, and build the thing in Aaron's garage. The box also has to be hermetically sealed and flooded with argon to work correctly. Aaron also makes some unconventional modifications to the box - "It looks like a dog digested it."

While experimenting, Aaron and Abe discover that the machine works. They put a blue weeble inside the box and register that it has decreased in mass. (While fiddling with the device, Aaron pokes his hand right the way into the field and Abe puts his hands over it to drop punched holes into the field. This becomes significant later.) Aaron and Abe instantly recognise the limitless applications and value of the device they have built. They immediately cut Robert and Philip out of the loop, saying that Aaron's garage has to be fumigated.

But at the same time, Aaron and Abe also realise that if they go public with their new invention too quickly, someone like Platts will take advantage of them again. They need to fully understand it first - which they don't.

Several months pass. The four men get funding from a Thomas Granger, while Abe establishes a relationship with his daughter, Rachel. (Aaron is of course happily married to his wife Kara, with a daughter, Lauren.) Abe tries to figure out how, exactly, the device does what it does - and he fails.

This is now March.

Monday (video time code: 18:36)

The first bench scene: Abe approaches Aaron one morning. Aaron is listening to March Madness on an earphone (and continues to do so for the rest of the day). Abe persuades Aaron to take the day off work, then he leads Aaron through a series of discoveries that he has made.

After repeated experiments on the weeble, Abe realised that a weird fungus was growing on it. He took it for analysis and was told that the fungus was perfectly ordinary, but that the amount of growth he had seen was consistent with years of time passing, not days. Suspicious, he put his wristwatch in the box. He discovered that what they had built was a time machine, which works like this.

The two of them immediately reason that if an intelligent agent was put inside the box, it could deliberately exit the box before it entered, travelling backwards in time. Abe then reveals to Aaron that he has already done this:

Abe built a coffin-sized time machine, which we shall call Box A, and placed it in a unit at a self-storage facility.

At 08:30 Monday, Abe primed Box A to activate itself in fifteen minutes.

He drove away from the self-storage facility and isolated himself at a hotel in Russelfield.

The box activated at 08:45 and was completely powered up at 08:49.

At 15:15, Abe returned to Box A and switched it off. It took another four minutes to power down completely. As it powered down, he climbed inside.

Abe waited six and a half hours (in the film the figure is repeatedly stated as "six hours"). At the correct time, he climbed out of the box just after it was activated - at 08:45 Monday.

Abe then approached Aaron for the first bench scene.

Now it's 15:15 Monday again, and Aaron and Abe-2 are able to watch Abe-1 return to Box A, climb in, switch it off and disappear into the past.

Tuesday (31:22)

Abe shows Aaron that he cunningly made a single excellent stock trade during Monday too.

On Tuesday, Abe goes through the same routine but this time Aaron insists on following along. By now, Aaron already has his own box built: Box B.

They switch on the boxes at 08:30 Tuesday, hide at the hotel all day and then return to the boxes at 15:15. Abe departs Box A at 08:45 Tuesday as expected, but Aaron gets jumpy towards the end of the ride, and exits Box B a minute or two early (or, from Abe's perspective, a minute or two late), suffering a severe physical reaction. The time is 08:50 Tuesday morning.

The dialogue during these scenes reveals a few more noteworthy facts.

Abe and Aaron are trying to modify history as little as possible. They isolate themselves at the hotel in order to minimise the effect. In particular, if they were to accidentally prevent their doubles from departing the timeline as scheduled, this would present a major problem, since there would now be multiple Aarons/Abes.

The other important line is "the boxes are one-time use only". What Aaron means by this is that after you have climbed out of a box, you CANNOT go back to it later, switch it off and climb in a second time - because that's what your past self did. You cannot use the same box to continuously loop through the same day. This is not actually true. For the purposes of this plot summary, however, all we need to know is that Aaron and Abe both believe this is true and operate under this assumption.

They make some more money on the stock market. That evening, they have a slightly drunken conversation with Aaron's wife Kara about the prospect of having unlimited wealth. Aaron raises the hypothetical of punching Joseph Platts in the face, then going back in time and telling himself not to, making it so that it never happens. Abe says they "can't do that", not because it's morally wrong to punch Joseph Platts in the face, or because Aaron can't tell Kara about the time machine, but because this would result in there being two Aarons. Which is bad.

"But the idea had been spoken. And the words wouldn't go back once they had been uttered aloud."

Kara also mentions a mysterious noise in their attic. Birds? Rats?

Wednesday (42:00)

The same routine again.

Aaron and Abe argue at the supermarket and the gas station that morning about paradoxes, free will, paranoia and predestination. One particular point that Aaron raises is the problem of living in a universe which has been engineered by somebody else. At the hotel, and then later on Wednesday afternoon at the library, Abe and Aaron discuss the problem that Aaron is keeping the time machines secret from Kara. They also discuss the problem of Robert and Philip. They agree to give them a certain amount of patent rights and/or equipment and/or cash in order to salve their consciences instead.

They loop back in time as normal. At 08:15 Wednesday, shortly after getting out the machine, Aaron is bleeding from his ear.

That day, make their successful trades. In the afternoon, they finally admit that the garage has been "sprayed", and work at the garage with Robert and Philip resumes. Robert and Philip have now received their gifts from Aaron and Abe.

Robert reports an interesting story. It seems that Monday night was Robert's birthday party. Abe wasn't there, but his girlfriend Rachel was there. So was Rachel's ex-boyfriend, who walked into the party brandishing a shotgun. So was Aaron, who by all accounts risked his life to defuse the situation safely.

On Wednesday evening, while Aaron and Abe are outside looking for Aaron's missing cat, Abe is angry that Aaron, a family man, risked his life in such a way. Abe is genuinely confused that Aaron acted so uncharacteristically irresponsibly. Aaron makes excuses and claims that since the discovery of the time machines he is seeing the world differently, referencing their conversations of earlier in the day. However, this does not fully explain his actions.

Thursday (48:45)

The same routine again.

During the day spent at the hotel, Aaron's cell phone rings. It is Kara, asking about dinner. This is a mistake, since Aaron is supposed to be sequestered. Abe tells Aaron not to bring the cell phone back in time with him - this is a perfectly sensible way to avert the possibility of a paradox.

They loop back in time as usual. On the second time through Thursday, Aaron watches a sports match (whose outcome they already know) while Abe eats a muffin. Then, on the way to a restaurant, Aaron's cell phone (which he has foolishly brought back in time with him) rings again.

This is a problem, and a critical turning point in the film. There are two Aarons at this point (one at the hotel), and, due to Aaron's clumsiness, two of his cell phones (one at the hotel). If the phone in Aaron's hand is ringing then, so Aaron and Abe reason, the phone in the hotel cannot be ringing. Symmetry is broken and history has changed. History can be changed.

Friday (52:10)

At about 02:00 on Friday morning some kids set off car alarms outside Abe's home. Abe goes to Aaron's house and gets him out of bed. Abe reveals that he has been routinely turning the boxes on at 17:00 and turning them off the following morning.

Abe then puts forward a confusing and potentially dangerous plan to visit Joseph Platts at his home, punch him in the face, then, around 03:00 Friday, to use these boxes to go back in time to 17:00 Thursday and make sure that neither the car alarms nor the punching happen. In theory, as a result, both Aaron and Abe's doubles would stay in bed all night, get into their boxes at 15:15 Friday as normal, and leave this timeline permanently, leaving just one of each of Aaron and Abe behind.

As they climb into the car, however, they realise they are being followed by Thomas Granger, Abe's girlfriend's dad and the project's main source of funding. Granger has several days' growth of beard on his face - but Aaron last saw him at 18:00 Thursday, when he was clean-shaven. Abe phones Thomas Granger's number and the guy who answers is indeed Thomas Granger... but he's not the guy who is following them. Something really weird is going on. This man is a different Thomas Granger who has come back in time using one of the boxes, probably exiting the box at 17:00 Thursday when Abe switched them on.

Aaron runs after Granger and when they get close to one another, Aaron trips and falls while Granger falls completely unconscious. They put Granger to bed at Abe's house; Aaron cannot approach him without somehow knocking him unconscious. They check that the boxes are indeed turned on. Aaron proposes shutting them off to see if Granger is inside, an act whose consequences would be exceedingly difficult to guess at. They do not do this.

Why has Granger come back in time? Obviously at some point in the future, Aaron or Abe told Granger about the boxes. Then, something happened to prompt Granger to head backwards in time to this point (the earliest he can go) and start observing them. They conclude that the situation would have to have been a real emergency but they have no clue what it could possibly be. "The permutations were endless." History has definitely changed now that Granger has come back, but they have no way of guessing whether the emergency in question has been fully averted by his brief interactions with them and the rest of the universe - he has only been out of the box for about eight and a half hours.

And so Abe loses his nerve.

It is now revealed that there is a failsafe box, built by Abe, in a second storage unit. This box has been running for 3 days 22 hours - in other words, since early on Monday morning. Abe started the box at about 05:00 Monday, then went back to bed until 08:30 when he returned to start Box A. At roughly 03:00 Friday, Abe returns to the failsafe box, with four days' oxygen and water and a small tank of medical-grade nitrous oxide, enters it and travels all the way back to 05:00 Monday.

Monday again (59:06)

Abe (now Abe Two) exits the failsafe box at 05:00. He travels to his home and gasses his double in bed with the nitrous oxide. He stashes his double in his bathroom.

Now we come to the second bench scene. As in the first bench scene, Aaron is listening to what is supposedly basketball on his earpiece. Abe Two is ill, after four days of very little food, and in shock, after violently gassing his double. Aaron, however, repeats most of the same lines as last time.

In fact, when Abe faints, it is revealed that Aaron is not listening to basketball. He is listening to a recording of that very conversation. How can this be? The recording must have been made in some previous timeline. This is not the original Aaron. This is not the original timeline. It never was. This Aaron has come back in time from the future.

"At this point there would have been some... discussion."

Aaron and Abe confront one another and explain everything that has happened. This is the most difficult sequence in the film to follow, partly because of the complexity of the plot but mainly because, due to the lack of CGI, it was impossible to put more than one Aaron on the screen at the same time. The two major discussion points are:

How? Aaron's line, "They are not one-time-use only. They are recyclable," means that although you cannot re-enter a box you climbed out of, you can bring another box with you, activate it once you climb out, and later use it instead, travelling back to the same moment in time again - or a few minutes later, at any rate. In some previous timeline, Aaron discovered Abe's failsafe box, anchored 05:00 Monday. He then got inside the failsafe and used it to go back in time, taking with him a second, folded-up time machine. This is the Aaron with the hood. On arriving home at 05:00 Monday, Hooded Aaron set up his second time machine as Failsafe Box B, let's say at 05:15 Monday. Hooded Aaron then went to his home and drugged his double's breakfast cereal milk, then stashed his comatose double in the attic. This is the noise that Kara mentioned on Wednesday night. This means that there are now two Aarons in this timeline, permanently. Hooded Aaron assumed his double's identity and recorded all of the week's conversations. Then, he used Failsafe Box B (remember: he cannot re-use Failsafe Box A since he already climbed out of it once) to go back in time to 05:15 Monday yet again. He took yet another time machine with him, which he set up as Failsafe Box C (05:30 Monday). He becomes Aaron Three, with the white jumper, no hood. Aaron Three arrives at his house just as Hooded Aaron has finished drugging and stashing Aaron Prime. Aaron Three tries to subdue Hooded Aaron in turn, but this time he is too exhausted, and Hooded Aaron wins. After a conversation, however, Aaron Three persuades Hooded Aaron to leave. There are now three permanent versions of Aaron: Aaron Prime, who is drugged in the attic; Hooded Aaron, who has left town; and the Aaron we have been looking at since the beginning of the first bench scene, with the headphone in his ear feeding him lines, is Aaron Three and always has been. Aaron Three has had a LOT of exposure to the boxes. This is why he began bleeding from his ear on Wednesday, and it also why his contact with Thomas Granger nearly killed them both. It is Hooded Aaron who is the narrator of the story. The "primer" of the title is Hooded Aaron's phone call to Aaron Prime. So which box did Abe use to come back in time? Logically, Abe must have used Failsafe Box C, since Failsafe Box A contained Hooded Aaron and Failsafe Box B contained Aaron Three. How did that happen? Aaron must have SWAPPED Failsafe Box A and Failsafe Box C. The box that Abe believed was Failsafe Box A (anchored 05:00 Monday) was actually Failsafe Box C (anchored 05:30 Monday). This is not seen or even alluded to in the film, but it is necessary to resolve this plot hole. Why? Problems of logistics aside, the last remaining question is why Aaron chose to come back in time so far, sacrificing so much, permanently duplicating himself twice. What is he trying to set right, exactly? The key to all of this is the party. It is obvious, though left largely unsaid, that when Rachel's ex-boyfriend walked into the room with a shotgun, things could have gone considerably worse. Aaron Three, we remember, risked his life to successfully defuse the situation. We now understand why he would take this risk. There are two other Aarons in this timeline, one of them being Aaron Prime. Aaron Three does not matter - he is a non-person, a walking dead man, and he has no right to Aaron Prime's family. He has no life to risk. If I may jump ahead in the film slightly, the basketball scene (which takes place sometime in the middle of Monday) is also important. This scene further establishes that it was Aaron who originally invited Will, Rachel's ex-boyfriend's cousin, to the party - and that it was Aaron who suggested that Will should bring Rachel's ex-boyfriend with him. In other words, whatever originally happened at the party was indirectly Aaron's fault.

Aaron Three thought the problem permanently settled. But the fact that Thomas Granger came back in time to 17:00 Thursday indicates that it was not, and something bad was still looming in Aaron and Abe's future. However, it is Monday morning again, and both Aaron Three and Abe Two are prescient now. They decide to engineer the situation to end better this time, with Rachel's ex-boyfriend actually arrested and jailed.

By Monday afternoon, Aaron and Abe are both suffering from the effects of a great deal of time travel - they are unable to write correctly. Remember when they put their hands into the machine?

At this point, the narrator, Hooded Aaron, reminds us that HE, of course, does NOT come from a timeline where everything worked out perfectly. In fact, he was never originally at the party. He has no idea how long it will take for Aaron Three to "reverse-engineer a perfect moment". From what we see in the film, though, for Abe Two and Aaron Three, it appears to work first time. The jealous ex is arrested and jailed. The End.

On Monday night Aaron Three crashes at Abe's house. Abe Two cannot sleep. And with that problem resolved, everybody lives happily ever after.

With the following exceptions.

Tuesday again (1:09:28)

Aaron Prime wakes up in his own attic after being drugged for 24 hours by his double.

Abe Prime wakes up in his bathroom after being gassed for 24 hours by his double.

There are three running failsafe boxes which evidently nobody has thought to shut down, in addition to Abe Prime's original Box A, which hasn't been activated yet but is nevertheless operational. "They'll be building their own boxes in another day. And [Abe Prime] already knows what they built."

Aaron Three and Abe Two wind up at the airport. Aaron is going to steal his double's passport and leave the country, because he can never go home. He has lost Kara and Lauren to Aaron Prime. Abe, meanwhile, is going to stay behind so he can sabotage their doubles' attempts to build the time machines. And, more sinisterly, stay close to Kara and Lauren. And protect them from Aaron Three. What?

And finally, on the other side of the world, Hooded Aaron makes his phone call to Aaron Prime. Maybe Aaron Prime records it and believes it, maybe he doesn't. Hooded Aaron explains the entire story, including why he drugged Aaron Prime, and thus "[repays] any debt I may have owed you".

"You will not be contacted by me again. And if you look, you will not find me." Hooded Aaron hangs up, and begins construction on a time machine the size of a warehouse. The End.