Complex sentence: Wellek and Warren view works of literature as pieces of "imaginative literature" which gain artistic merit from the works' coherence and complexity, contrasted from scientific and other papers by the use of connotative (non-literal) language and expressive content.
Split into simpler sentences: Wellek and Warren limit their definition of literature to pieces of "imaginative literature", which can gain artistic merit from their coherence and complexity. The language in literary works is contrasted from scientific and other languages by the use of connotative (non-literal) language and expressive content.