In high school (and for the SAT) you're taught to do 5 paragraph essays which have a structure that looks like this:
2: First detail to support argument
3: Second detail to support argument
4: Third detail to support argument
But that's also kinda BS.
5-paragraph essays are the worst, and in my experience usually look like this when students produce them:
P. 1. Intro: Here's an overly general, usually obvious, pretty uninteresting point.
P. 2: Here's one reason why my point is true.
P. 3. Here's another reason why my point is true.
P. 4. Here's another reason why my point is true.
P. 5. Thus, my point - let me just repeat that in case you missed it - is true.
I get why the 5-paragraph model is used as a teaching tool - it helps very young writers understand that an essay needs to revolve around a unified point, and every paragraph must link to that point in some way. Body paragraphs in this model, too, all follow the same basic structure (always beginning with a topic sentence), so students learn that paragraphs, too, like the overall essay, need to offer unity and coherence around a single point.
One key problem with the model, though, is it teaches students they merely need to repeat a point or make a list of points, and so the thinking it produces is repetitive and simplistic (not to mention boring - for both writer and reader).
So, I spend a lot of time talking with my first-year college students about un-learning 5-paragraph writing/thinking and considering what it means to develop or evolve a complex idea. An essay still needs to be coherent (all the parts have to fit together); it needs a thesis (something it sets out to demonstrate, prove, support) - but the thesis is an idea
, not just a simplistic statement, and just like real ideas (those that people might actually care about), the path to that idea can look a lot different, depending on the thinker/writer, depending on the audience, on the topic, and on a lot of things. Within that context then, assuming an essay develops an idea, an essay can have 5 paragraphs or it can have 20; some paragraphs can be long, and some can be short; some paragraphs describe a thing; some paragraphs are a series of questions; some paragraphs offer an extended syllogism. The paragraphs depend, really, on what the unique idea being developed in the individual essay requires.
That kind of writing, with no rigid model to squish an essay into, is harder - because it requires deeper, more complex, creative thinking - but it's also a lot more exciting because sometimes/often, you don't know exactly where you'll end up in your thinking/writing
(not true for the 5-paragraph model, where you already know that the conclusion merely repeats the introduction).
I will agree though, Junior, that it takes a very good writer to make a very long paragraph successfully coherent - if a paragraph is, essentially, a unit of thought, offered up for the reader to digest, one unit at a time, a long paragraph can easily lose coherence; the logic and unity can break down if the thinking isn't crystal clear - the unit of thought becomes a mush of a bunch of thoughts. And yes, while we could - and probably should - talk all day about what "good writing" is (happily, a frequent, repeated conversation in my English department), it's a real pain, as a reader, to try to digest a bunch of thoughts all mushed together, rather than a single thought at a time. I think of a paragraph as a kind of extension of friendship to the reader: "here, I won't shove all my thinking at you at once; I'll give you one bit at a time, and we'll get there, step-by-step, together."