If a literary system is the environment in which a piece of text comes into being, then literary forms are
the building blocks of that environment. These forms are idiomatic ways of writing, authorial tricks that have built up over the years and codified themselves into common practice,
tools with which to make meaning. Taken in aggregate, they form a system of rhetoric, a
literary system.
An example: In mathematics there is a method of proof called
reductio ad absurdum, by which a mathematician demonstrates the impossibility of some hypothesis by proving that if it were true, then a logical impossibility (the absurd) would also be true, and therefore it is false. Now, the mathematician does not have to explain this endeavor every time she attempts it, by merely mentioning the
reductio her audience will understand what she's trying to do. This method of framing the proof is an example of a literary form that adds expressive power to the system of mathematics. There are many others.
As with all abstractions, you gain in expressiveness by using a literary form, but
lose in detail. The
reductio encompasses a wide array of proofs, but is not specific to the explanation of any particular one, over others. In computer programming, the expressive power of these forms is made literal. When a programmer uses a so-called "high level" computer language, she can employ a whole horde of algorithms and data structures with a single instruction, but knows very little about what the machine is up to. With novels, as an author employs more expressive literary forms, she can assume less and less about the exact thought processes that will eventually take place. A powerful word at the end of a novel can set a host of thoughts, repercussions and emotions through the mind of the reader. Instead of writing out the details explicitly, the form shapes the meaning.
The forms can, of course, be used in combination. When you come to the end of a book, having devoured it, feeling like there was not a wasted word, you've experienced the epiphenomena that manifests itself as a result of the interactions of literary forms.
