The limit that separates literary language from other forms of language is blurry. Many works of scientists and journalists can be considered true pieces of literary work.
The extension of the text is not a key feature, since it’s so variable; it can range from a few verses to a hundred or thousands of pages.
That said, a literary text has very peculiar internal characteristics that are also very hard to point out. It shares these features with other types of texts: advertising, slogans, journalism, etc.
1. Uninterested nature
A literary work can be read under multiple interpretations, as many as readers and listeners are out there. This does not interfere with communication; on the contrary, many readers who are interested on a specific work often do not understand it, or understand it in a very superficial way. But communication is still satisfactory. This couldn’t happen with ordinary messages with a practical goal, since it would lead to mistakes.
Words acquire new meaning. The reader gives the whole text a meaning that goes beyond that of isolated words. The literary work is as much direct transmission of content as it is a suggestion. Some consider that a literary work consists of two parts: writing, that of the author; and reading, that of the reader. In this sense, the readers complete the work, and therefore have to know cultural and linguistic references implied in the work.
The author always looks for some degree of originality. In order to do that, one creates a personal language, and observes reality from new perspectives, trying to express nuances, subtleties, and depths that aren’t easily accessible to anyone.
5. Literary devices
According to traditional rhetoric, all expressive sources can be figures of speech: syntactic, semantic, and phonetic. They are used to decorate and intensify the language. Many of them are based on repetition and parallelism. Repetition produces rhythm in both prose and verses. It can light up any type of prose, but abusing rhythm can risk falling into excessive musicality and nonsense.
Many hundreds of literary devices have been described.
One of the devices that’s most characteristic of literary writing is special adjectives, such as epithets. These are ornamental adjectives, not strictly needed for the comprehension of the message. A good writer always tries to avoid trivial epithets, and to generally disregard those, which do not produce any new effects on the reader.
Literary language has a high degree of elaboration.