This article, from Gloria T. Delmar, originally appeared on the Philadelphia Writers Conference site in 1998.

The idea of "writing to formula" turns off many writers. But the fact is, that most writing does indeed fall into certain broad "concepts" or "plans." It's not counter- productive to understand these accepted schemes for making a piece of writing make sense for the intended reader (and first, the intended editor). Don't let yourself get locked into seeing formulas or concepts as negative; the reason they've been defined is because they work--and that's positive synthesis.

Mathematical Patterns Applied to Fiction

1+1=2

 This equation represents the "satisfying" or "happy-ending."
At least three-fourths of all modern, commercial short stories and a large percentage of longer stories, are written on this pattern.

1-1=0

 This equation represents the "unresolved" or "fitting punishment ending."
A much smaller percentage of "literary" stories follow this pattern.

"1" represents basic emotions:

 love, hate, fear, anger, courage, security, greed, piety, pride, honor, generosity, miserliness, honesty, good, evil, friendship, ambition, desire, patriotism, etc.
or conditioned emotions:
parental love, sacred love, profane love, etc. (ETC. for all basic emotions.)

To make a strong story, you need a strong conflict between two emotions. You can match two simple emotions, two conditioned emotions, or a simple emotion and a conditioned one. Though the + or - signs in the mathematical pattern might be read as "versus" the "plus" and "minus" concepts reflect the nature of the problems and conflict, and forecast the outcome.

Short Story:

Single viewpoint character: entire story takes place in a short period of time;
Single plot: focuses on a single theme.

Novel:

May be single or multiple viewpoint (but one viewpoint per scene); story may take place in a short period of time or range over years; may have main lot plus several sub- plots; may focus on a single theme overall, or include more than one.

Aristotle's Rules of Tragedy

amagmorsis:

revelation of true identity of person previously unknown.

catharsis:

arousal of pity and fear to enlarge spectator's outlook.

hamartia:

called "tragic flow" inherent defect in the hero.

periteteia:

shift of the tragic hero's fortune from good to bad.

verisimilitude:

"resemblance of reality" in drama or non-drama.

Read the rest of the article, which includes The Who What When Where Why and How formula, The Thirty-Six Dramatic Situations, The Seven Deadly Sins and The Seven Deadly Sins of Writers, on the Philadelphia Writers Conference site.