Can we see a break-down of the concepts behind the Multiple Acts school of writing? I've had the idea of three acts only shoved down my throat for years and it feels wrong to try to shoehorn a story into this particular artificial construct. Is there some magic number of acts, or do you just need to make sure your story has a beginning and an ending of some sort and build from there or something else entirely? -- quitwriting

Completely agreed. I don't fully understand what makes one act disparate from the next. -- erranthope

I'd be interested to see this as well. -- stormwyvern

I currently define an act as when the status quo changes into something else, and those changes are irreversible...How many acts, though? My answer right now is "however many you need to tell the story". -- Kent M. Beeson

Let me answer this the best way I know, by telling a story:

Often in my work, a producer will say "Let's make it like Star Wars," or "Let's make it like Jaws."  So I've watched both of those movies many times from a lot of different angles and, over time, noticed something fundamentally different about their structures.

Star Wars Episode IV and Jaws are both 2 hours long. Divided into three acts, that would make each act about 40 minutes. There's no rule saying that each act must be of equal length, but let's face it, if your acts get too long or short the narrative starts to feel lopsided. So, when I sat down to study the structure of Episode IV, I kept my eye on the DVD readout and tried to see when things would start to feel "different."

Act I of Episode IV has one agenda: to get its protagonist, Luke Skywalker, off Tatooine. Everything that happens in the movie up to that point is rushing toward the goal of getting Luke Skywalker off Tatooine. As Mr. Beeson notes, this change is irreversible. Luke is leaving Tatooine and he ain't never going back. If Luke could stay on Tatooine, the rest of the movie wouldn't need to happen and the Death Star would never get blowed up.

So it is imperative that Luke leaves Tatooine and never comes back. How does the screenplay get that to happen? It has Darth Vader board Princess Leia's blockade runner, which forces her to hide the plans to the Death Star inside R2-D2, which forces R2-D2 to hop in an escape pod with C-3PO and blast off, which causes them to fall into the orbit of Tatooine, where they crash-land in the middle of nowhere, which causes them to wander in the desert and separate, which causes R2-D2 to get kidnapped by Jawas, which causes the Jawas, who are scavengers and used-droid dealers, to sell R2-D2 and C-3PO to Luke's Uncle Owen. Meanwhile, Darth Vader is no dummy, and he sends troops down to Tatooine to look for those goddamn droids who made off with his Death Star plans. R2-D2 goes pouncing off one night, which causes Luke to follow him, which leads him to meet Obi-wan, who tells Luke that he is no ordinary farm boy, no indeedy, he is the son of a Jedi Knight. Luke sees the message R2-D2 is carrying for Obi-wan, which causes him to fall in love with Leia and with the whole idea of rebellion and adventure and all that stuff, which causes him to realize the stakes he's playing for, which causes him to rush home to find that his aunt and uncle have been killed by Darth Vader's troops, which finally, at long last, makes him realize that HE MUST LEAVE TATOOINE AND NEVER RETURN.

Act II is then: "Respond to the Message," and the point of Act II is to make Luke miserable.

Princess Leia called Obi-wan, remember? So what shall Obi-wan do? He will respond to her message -- he will grab Luke and the droids and hire a fast ship to take him to Alderaan, where Leia lives. But -- aha! -- complications ensue. Obi-wan hires his ship and flies to Alderaan, only to find that Alderaan ain't there no more, but the Death Star is. They get sucked into the Death Star, and their goal changes -- now they must "get off the Death Star." They're still on their way to help Leia, they've just been sidetracked by this Death Star thing and the whole no-Alderaan problem. While Obi-wan goes sneaking off to dismantle the Death Star's tractor beam, Luke and Han and Chewie (the pilot and co-pilot of the ship Obi-wan hired) discover that Leia is, in fact, here on the Death Star! What fortune! So Han and Luke and Chewie go off to rescue Leia whilst Obi-wan sneaks around being a Jedi. Luke springs Leia, Obi-wan dismantles the whatsit, and they meet up back at the ship. But argh! There's that Darth Vader guy, and he seems to know Obi-wan somehow, and they fight and Vader kills Obi-wan. This is what we in the business call the "End of Second Act Low Point." Everything had been going so well for Luke, he got his adventure and his princess, but now his mentor is dead and he's being chased by an entire fleet of Darth Vader's army guys. So, again, the act break leaves its protagonist irreversibly different -- Luke not only can't go back to Tatooine, he can't go back to being mentored. He's all alone now, the Princess ain't never going to go for a guy like him and he's never going to make it out of this situation alive.

Act III is then "Luke Triumphant." Luke, who has had everything he knows taken away from him, twice, now must survive an ordeal by fire, join up with Leia's rebel forces, turn around and blow up that goddamned Death Star and show that fucker Darth Vader a thing or two. At the end of Act III, Luke is about as far away from the simple farm boy he was at the start of Act I as he could be.

So that's all very clear, and very classically constructed.

Now then: Jaws is also two hours long, and when I first sat down to analyze it I assumed that it, like Episode IV, was neatly divided into three acts of equal length. (For a full breakdown of Jaws, begin here.) Now, at the 40:00 mark of Jaws, Chief Brody is sitting in his dining room talking to Hooper about sharks. I thought, well, that's no act break, let's keep going. After chatting with Hooper, Brody goes down to the docks to cut open the tiger shark. And I thought "well, okay, that's an irreversible change, now Brody knows that the big mean shark is still out there.

Then something strange happened.  At exactly the hour mark, the guy gets his leg bit off in the estuary and Brody stands there on the beach and stares out to sea.  And I thought "hey, that feels like an irreversible moment as well, but it's coming only fifteen minutes after the last one."  What's happening at that moment?  Why is Brody compelled to stare out to sea when there's a dead guy in the estuary and his son lies at his feet in shock?  I realized that, at that moment, Brody is realizing that he's got to go out there.  Up to that moment, he'd been doing everything he could to "manage" the situation, to play ball, to balance the financial needs of the town with the reality of the shark, but now, god damn it, he's got to go out there and kill this thing.

I went back and started watching the movie again from the beginning.  What's the first thing we learn about Brody?  The first thing we learn about Brody is that he's new in town.  He used to be a city cop, now he's a country cop, and he's not used to country ways.  He is, as we say in story meetings, a fish out of water.  Why is this significant?  Because Chief Brody, protagonist of Jaws, is afraid of the water.  He's taken a laid-back job in a small town on an island with the expectation that he would never have to go in the water.  Now this goddamned shark comes along, and Brody does absolutely everything he possibly can to deal with the situation, provided he doesn't have to go in the water (this is why he gets roaring drunk before going out with Hooper at night).  When he's set up snipers and lifeguards and patrol boats and everything else and it still doesn't work, when all his efforts to protect his town and family come to nothing, he realizes that he must go out there and do this thing, he has no choice.

And I thought, well, but that would mean that the first act of Jaws is an hour long, and that can't be right.  And I kept pushing ahead into the narrative, and I saw that, at almost exactly 1:30:00, it's night time and Brody and Hooper and Quint are trading their war stories, and they start singing, and they're bonding and everything is going well, and the shark comes pounding on the side of the boat.  And the rest of the movie plays out in something close to real time as Hooper's cage gets built and trashed, Quint gets eated and Brody realizes that he, he alone and nobody else is going to have to kill this thing, or else all is lost.  Check out the way Brody, still, does everything he possibly can to stay out of the water, climbing up and up and up as the boat sinks.  Spielberg's choice to make Brody afraid of the water seems silly and arbitrary on paper, but it transfers directly into the audience's consciousness, and the visual scheme of the movie is: if you're out of the water, you're okay, if you're in the water, forget it, all bets are off.  Spielberg manages to make the water itself a terrifying vision of doom.

So now I had a movie with an hour-long first act, a half-hour-long second act and a half-hour-long third act.  And I thought, well, that doesn't feel right.

So I went back to the beginning of the movie again and checked around the 30:00 mark to see what's happening there.  At 30:00 or so, the tiger shark is caught and Brody has a sense of relief that maybe this whole thing might just blow over.  And I thought "Well, that's a nice beat but it's not irreversible," very much so as it turns out.  And I kept watching, and here comes Hooper, and there's some business with the tiger shark, and then Mrs. Kintner shows up.  Mrs. Kintner is the mother of the boy who got eated earlier in the act, and she's just come from his funeral.  And here, in Brody's moment of triumph (I solved the problem and I didn't have to go out on the water!  Yay!) Mrs. Kintner shows up and slaps him in the face, really clubs him, and then walks off.

And I thought, well, that's a scene-ender for the ages, but is it an act break?  Is it irreversible?  And the next thing that happens is Brody is getting drunk at home and chatting with Hooper and this is where we came in.

So I thought more about Chief Brody and what his job is.  His job is to protect the citizens of Amity, and so far in the narrative he's succeeded in doing that by playing along, by swallowing his pride and buckling under the demands of the mayor.  But the slap from Mrs. Kintner, even in the moment of his triumph, tells him that "playing along" is not the same thing as "doing his job."  Mrs. Kintner tells him that he is responsible, and he'd better start acting like it.  No wonder he responds by going home and getting drunk -- this isn't what he signed on for at all.  Chief Brody wanted a lazy job where he could relax after a career in the big city, he didn't come out here to Amity to be responsible.

So I realized that Jaws, contrary to the thing that gets hammered into film students' heads every semester, does not have three acts, it has four.  Act I gets Brody to the point where he has to realize his personal responsibility to the people of Amity, Act II gets him to the point where he must reconcile his fears with his responsibility, Act III sends him out on the water (that is, facing his fears) with two "experts" to help him continue to avoid responsibility, and Act IV takes away all his help, whittles away at all his resources until it is, literally, him and the shark.

Once I came the realization that Jaws has four acts instead of three, I started looking at all of Spielberg's other movies and seeing that most of them, almost all of them really, follow a similar structure.  Spielberg seems to get uncomfortable if his acts go much longer than 30 minutes, and so a two-hour movie has four acts, a two-and-a-half hour movie has five acts, and so forth.  (Munich had me baffled, with its ten-minute sequences that fill up its middle 90 minutes, and took a lot of thought to figure out.  Close Encounters, not so much -- the act breaks are practically announced with triumphal fanfares.)

Studying the act breaks of a movie is a hugely helpful tool in figuring out what the screenplay is "about."  Me, I'm suseptible to the lure of gorgeous photography, crisp performances and swelling music, not to mention changes in location, so it's easy for me to get lost in a film narrative and lose track of the act breaks.  Sometimes a climactic cinematic moment will indicate an act break, sometimes it won't, sometimes that wonderful moment will just be helping to get the protagonist from point A to point B in an entertaining fashion. 

What studying the act break does is reveal the journey of the protagonist -- at one moment, the protagonist is one person, and in the next moment he is another, and that change is irreversible.  The path of the protagonist is the meaning of the movie -- that's the important thing, everything else is in the service of the delineation of that concept.

There is no "magic number" of acts, but I'll tell you, once you get past five an audience will start to feel like you're bullshitting them.  Act breaks put an audience through an emotional wringer, and when you have too many of them the audience starts to feel exhausted and your movie feels long.  Too few and it feels weird.  Three is taught because a lot of movies follow it, and the thought of three has become so prevalent that one has to be Steven Spielberg or somebody to make a movie differently structured.  I've sat in pitch meetings for 13 years now and I've never once had a producer suggest a four-act or five-act structure, even though they are perfectly viable alternatives.