Aside from being one of the formative writers of the 19th century, E. Poe also attempted to address what he thought of as the proper themes and techniques that made his writing resonate with people the world over. Concerning prose, Poe settled on two ideas that he felt should be the basis of prose, the themes being those of unity and vagueness. In looking at the "The Facts in the Case of M. Valdemar," we see Poe's own use of vagueness and unity in his work.
Beginning with vaguenes, we see Poe's peculiar alternations from detailed, though fictitious, medical descriptions, to only the barest use of language to portray the trance of Valdemar. At the beginning of the piece Poe describes the ravages of Valdemar's unnamed disease. This is merely setting the stage for the plot. When the narrator brings Valdemar to the trance, suspending him between life and death, Poe provides almost no detail as to the horrors being expirienced by Valdemar. Using the vagueness, Poe allows us to fabricate the details ourselves, leaving the reader with a vision infinately more frightening then anything he could have written.
On the topic of unity, ". . .M. Valdemar" presents us with a very simple story, without much going on. There is a unity in the story in that it does not deviate from the central plot, the mesmerization of Valdemar. There are no other plot threads and very little characterisation. The characters seem less as people, but more as bits of scenery. .
As with many of Poe's stories, ". . . M. Valdemar" is an excellent example of his concepts of literary vagueness and unity. These concepts allow the reader to stay focused on the main theme, while forcing them to create a lot of the horror for themselves.