How many "basic" plot lines are there? Depends on who you ask and how lossy their compression is.
Beside each master plot I've tried to describe it where the title isn't good enough, and provide a popular or well-known example. By doing so I'm not trying to be reductionist but rather illustrative. If you can think of a better one than I've listed, or can suggest something for one I've left blank, let me know and I'll consider dropping it in.
Oh, and before your author's hackles go flying, be forewarned that I'm not going to try and name The One True Number. I don't think such a thing would be useful. I've listed them because it's fun reading, and really useful to kickstart one's own imagination. Writing with them as proscription would surely be the death of creativity.
Ronald Tobias (see below) reports that Rudyard Kipling listed sixty-nine, but does not cite them.
The Stumpers Archive presumptuously adds a 37th to Polti's 36 plot lines, below.
37. Mistaken Identity (Trading Places)
George Polti proclaimed in his 1921 book The Thirty-Six Dramatic Situations that there were, as you'd imagine, exactly 36 dramatic situations, naming specific dynamic elements neccessary for each. He claimed to be trying to reconstruct the 36 plots that Goethe alleges someone named Carlo Gozzi devised, but it could be hearsay.
- Supplication (Persecutor, Supplicant, Power in Authority Whose Decision is Doubtful) (Antigone)
- Deliverance (Unfortunate, Threatener, Rescuer) (Roots)
- Crime Persued by Vengence (Avenger, Criminal) (Les Miserables)
- Vengance Taken for Kindred Upon Kindred (Avenging Kinsman, Guilty Kinsman, Remembrance of the Victim, a Relative of Both) (Not Without My Baby)
- Pursuit (Punishment and Fugitive) (Road Runner)
- Disaster (Vanquished Power, Victorius Enemy or Messenger)
- Falling Prey to Cruelty or Misfortune (Unfortunate, Master or Misfortune)
- Revolt (Tyrant and Conspirator) (Gladiator)
- Daring Enterprise (Bold Leader, Object, Adversary) (Jonathan Livingston Seagull)
- Abduction (Abductor, Abducted, Guardian) (The X-Files)
- The Enigma (Interrogator, Seeker, Problem) (The Matrix)
- Obtaining (Solicitor, Refusing Adversary) or (Arbitrator and Opposing Parties)
- Enmity of Kinsmen (Hatred OR Reciprically Hating Kinsmen)
- Rivalry of Kinsmen (Preferred Kinsman, Rejected Kinsman, Object) (GATTACA)
- Murderous Adultery (Adulterers, Betrayed) (Fatal Attraction)
- Madness (Madman, Victim): (Fight Club)
- Fatal Imprudence (The Imprudent, Victim or Lost Object) (Les Liasons Dangerous)
- Involuntary Crimes of Love (Lover, Beloved, Revealer) (Wilde)
- Slaying of Kinsman (Unrecognized Slayer, Victim)
- Self-Sacrifice for an Ideal (Hero, Ideal, Sacrificed)
- Self-Sacrifice for Kindred
- All Sacrificed for Passion
- Necessity of Sacrificing Loved Ones (Hero, Beloved Victim, Necessity)
- Rivalry of Superior and Inferior (Superior, Inferior, Object) (Nineteen Eighty-Four)
- Adultery (Adulterers, Deceived) (Madame Bovary)
- Crimes of Love (Lover, Beloved)
- Discovery of the Dishonor of a Loved One (Discoverer, Guilty One)
- Obstacles to Love (Lovers, Obstacle)
- An Enemy Loved Beloved (Enemy, Lover, Hater) (Romeo & Juliet)
- Ambition (Ambitious Person, Thing Coveted, Adversary) (Macbeth)
- Conflict with a God (Mortal, Immortal) (Jason and the Argonauts)
- Mistaken Jealousy (Jealous One, Object of whose possesion he is jealous, Supposed Accomplice, Cause or Author of the Mistake)
- Erroneous Judgement (Mistaken One, Victim of Mistake, Cause or Author of Mistake, Guilty Person)
- Remorse (Culprit, Victim or Sin, Interrogator)
- Recovery of a Lost One (Seeker, One Found)
- Loss of Loved Ones (Kinsman Slain, Kinsman Spectator, Executioner)
In his 1993 book Twenty Master Plots (And How to Build Them), Ronald B. Tobias suggests that there are twenty main ones.
- Quest (The Wizard of Oz)
- Adventure (Alice's Adventures in Wonderland)
- Pursuit (Bugs Bunny)
- Rescue (The Pianist)
- Escape (Escape from Witch Mountain)
- Revenge (The Count of Monte Cristo)
- The Riddle (The Matrix)
- Rivalry (GATTACA)
- Underdog (Seabiscuit)
- Temptation (Genesis)
- Metamorphosis (physical transoformation) (Metamorphosis)
- Transformation (abstract transformation)
- Maturation (Moonshadow graphic novel by John Marc DeMatteis & Jon J. Muth)
- Love (Anna Karenina)
- Forbidden Love (Gods and Monsters)
- Sacrifice (The Gift of the Magi)
- Discovery (Huckleberry Finn)
- Wretched Excess (Sid & Nancy)
- Ascension (The New Testament)
- Descension (King Lear)
Blake Synder says in 2005's Save the Cat! that there are obviously ten alive in Hollywood. (Examples his.)
- Monster in the House (Jaws)
- Golden Fleece (Back to the Future)
- Out of the Bottle (Freaky Friday)
- Dude with a Problem (Die Hard)
- Rites of Passage (Ordinary People)
- Buddy Love (Dumb & Dumber)
- Whydunit (JFK)
- The Fool Triumphant (The Jerk)
- Institutionalized (M*A*S*H)
- Superhero (A Beautiful Mind)
John Carroll says in 2001's The Western Dreaming that there are definitively nine.
- The Virtuous Whore (Pretty Woman)
- The Troubled Hero
- Salvation by a God (The Old Testament)
- Soulmate Love
- The Mother
- The Value of Work (Animal Farm)
- The Origin of Evil (Most creation myths)
- Self-Sacrifice (Muriels' Wedding)
Robert Blake also fits in the 9 category after he added one to Johnston’s 8, below.
9. The homeless loner: (The Flying Dutchman)
Denis Johnston argued that there were really only 7 core plots.
- Unrecognised virtue at last recognised (Harry Potter)
- The fatal flaw (Hamlet)
- The debt that must be paid (The Pied Piper)
- The love triangle (Le Morte D'Arthur)
- The spider and the fly (Labyrinth)
- Boy meets girl, plus obstacles (American Pie)
- The treasure taken away (loss, sometimes followed by search) ()
...and then added an eighth to accomodate all the Indiana Joneses and Forrest Gumps of the world.
- The irrepressible winner
In middle school you may have heard the conventional "versuses", which must have spontaneously generated in the collective uncounscious since I can find no attribution.
- (Wo)man vs. nature: (Moby Dick)
- (Wo)man vs. (wo)man: (Silence of the Lambs)
- (Wo)man vs. the (wo)environment (just kidding, jeez): (Joe versus the Volcano)
- (Wo)man vs. machines/technology: (The Golem)
- (Wo)man vs. supernatural: (Dracula)
- (Wo)man vs. self: (Dr. Jeckyl and Mr. Hyde)
- (Wo)man vs. god/religion: (Priest)
In 1959 Willisam Foster-Harris semi-comically outlined three in The Basic Patterns of Plot
- Literary "in which, no matter whether we start from the happy or the unhappy fork, proceeding backwards we arrive inevitably at the question, where we stop to wail": (Ulysses)
Colin Jacson, while web publishing, agrees with the number, just not the categories.
- Hubris, the sin of pride which is punished (The Illiad)
- Discardation, the loss of something (High Noon)
- New Order, the attempt to achieve change (Pinnochio)
In Poetics, Aristotle said there were just two categories we need to be concerned with.
- Comedy, in which the hero gets what the hero wants. (The Clouds)
- Tragedy, in which the hero doesn't. (Oedipus Rex)
Tobias even admits that his 20 can be reduced to two, but he divides them differently.
- Plots of the body, which are all action.
- Plots of the mind, which have pith.
Joseph Campell in his 1949 book The Hero with a Thousand Faces said there was actually only one called The Hero's Journey (introducing the concept of the Deep Structure to the literati of the time), and unduly influencing Disney, via a famous memo to executives by Christopher Vogler, up until the present day.) The seminal example: Star Wars, which Lucas deliberately structured around The Hero's Journey.
But Campbell was talking about myth in particular and admitted that there were countless permutations. And really, each of those parts could be a basic plotline, couldn't it?
Much more succintly, Kurt Vonnegut (as recently as 2001, when he was accepting the New York State Author title) beat everyone in the reduction game and stated that there was just one, "man in a hole," essentially saying that all narrative was about conflict resultion in some form.
And then he added "boy meets girl," qualifying that it needen't really be about a boy.
Or a girl.
Oh to hell with it.