The shelves of your local bookstore are littered with books of advice for would-be writers, making it impossible to discuss craft essays in general. So I'm going to zoom in on one particular craft book - the grandaddy of all craft books - Aristotle's Poetics.
There are lots of things we have to keep in mind with Aristotle. For openers, he never intended to write a craft book; as in so many other fields of knowledge he appears just to be laying down taxonomies and general principles. And his legacy is, let us say, spotty. In the field of dentistry, he helpfully tells us women have fewer teeth than men. In natural science, he informs us that snakes have no legs because their bodies are too long. All vertebrates, he points out, have two legs, four legs, or none. Since snakes' bodies are too long to be supported by two or four legs, they have no legs at all. (Actually, that last part makes a weird kind of sense.)
Lastly, Aristotle was only writing about one very narrow genre: tragedies, not even full-length plays, but one-acts he would have seen performed at the Theater of Dionysus. Aristotle had never seen a novel, short story, or movie. There were no video games in Aristotle's day. If there had been, he wouldn't have had time to come up with the thing about the snakes.
Having said all this, and made this lengthy preamble of caveats and disclaimers, I'm only going to look at one little bit of what Aristotle had to say.
He writes that tragedy is an "imitation of an action, that is serious, complete, and of a certain magnitude." The need for seriousness, when it comes to tragedy, goes without saying, which is probably why Aristotle felt called upon to say it. Writing a silly tragedy is out of the question. It's just too ambitious. Life itself is a silly tragedy.
The part about imitating an action is more key. What Aristotle meant by imitation of an action primarily had to do with "Perepetia" or Reversal of the Situation and a scene of Recognition. When it comes to aesthetics, Aristotle is on entirely different ground than with the natural sciences. Is isn't like pointing out snakes don't have legs; there are plays, plenty of them, that Aristotle says lack this all-important reversal and recognition. He doesn't claim that tragedies must contain these elements, but that they ought to. It would be as if living in a world where some snakes had no legs, some had two, and some had twelve, Aristotle said that the best kind of snake had no legs. Best under what criteria?
When Aristotle says the greatest tragedies have Reversal and Recognition, he means these are the best tragedies to him, and to the audience as far as he can tell. Even if Aristotle's tastes in this regard aren't universal and even if we cannot say they are to be preferred over other criteria, to the extent we share them - and personally, I share them whole hog - they tell us a great deal about ourselves.
We are interested in seeing stories where things change, and no amount of "characterization" can make up for a static plot line. In the case of tragedy, we like seeing things start out more or less hunky-dory and then go all kaflooey. (In comedy, although Aristotle does not deal with this, presumably we like to see things go from being totally screwed up to finally being screwed down again.) This need for temporality, for mutability and reversal is an interesting aspect of our nature. There's a Gahan Wilson cartoon of two bored-looking angels standing around in heaven, and one of them says, "I keep thinking it's Wednesday." That's the thing about us; we bitch if things go bad, but what we really can't stand is if they stay the same. I prefer a life with a certain degree of friction, failure, and frustration than an unbroken tableau of contentment.
Aristotle's dictum that the action be "complete" is intriguing too. Aristotle seems to be the first person to articulate that stories need a beginning, middle, and end. I agree with Aristotle's formulation, but how odd that we should have a taste for that. Where did we acquire it? What in our lives has ever occurred in such neat segments? Isn't life always a matter of vague "middles" without clear beginnings or definite ends? Oh, I know humans have plenty of beginnings and ends - birthdays, weddings, graduations, retirement parties, funerals - but most of these, when you think of it, are man-made contrivances. Nothing in Nature knows what "New Year's Day" means. These demarcations are as arbitrary, and strangely essential to our sense of well-being, as a five-act play with an intermission.
The Scene of Recognition is an interesting stipulation also. It's not enough for Oedipus to get bludgeoned by fate, he has to come to an understanding of what has happened and why, and more specifically, his own unknowing role in it. This is another anomaly that surely points to another desire that life does not fulfill. How often have we ever been lucky enough to understand why crap happens to us? Isn't it more the case that things rain down on us from space with no clear reason: old age, illness, death, loss? That these things are predictable and unavoidable makes them no less mysterious. Oedipus at least gets to say, "I screwed my mother! That's what went wrong! There was a curse! The gods had it in for me!" The rest of us, waiting for the day we'll see the spot on the X-Ray that will be the thing that kills us, waiting for the phone call that someone we love has died, waiting for the tsunami, the wildfire, the terrorist - the rest of us will have no such moment. We will live our lives as well as we can in the meantime, but that fell blade will fall, and when it does so, it will strike with astonishing abruptness and without explanation. Maybe this is why Oedipus can pull out his eyes. Once he has seen the thread that tied himself to his fate, he had already seen what the rest of us will spend our whole lives looking for.
Man. I got unexpectedly grim there at the end, didn't I?
Maybe another post, I'll talk some more about Aristotle, but I'll leave him alone for now.
Meanwhile, why don't you think about how come snakes don't have legs?