* Sound and Meaning: Poe emphasizes the importance of assonance and consonance for creating a specific mood and atmosphere. The raven's repeated "Nevermore" is a prime example of this, creating a chilling, monotonous sound that contrasts with the narrator's desperate pleas.
* Repetition and Variation: The repetition of "Nevermore" is itself a form of contrast. While it's repetitive, it also changes in meaning and impact as the poem progresses, shifting from a simple response to a haunting symbol of loss and despair.
* Darkness and Light: Poe also emphasizes the role of darkness and light in setting the mood. The poem takes place in a dark, gloomy atmosphere, which creates a stark contrast with the light and hope the narrator initially seeks. The raven, as a symbol of darkness, further emphasizes this contrast.
* Simple vs. Complex: Poe suggests a focus on simplicity and directness to make the poem more powerful. This directness creates a contrast with the narrator's increasingly complex emotional state, highlighting his descent into madness.
While Poe doesn't explicitly discuss the contrast in the raven's portrayal, these underlying principles of his "Philosophy of Composition" contribute to the creation of strong contrasts within the poem.
It's important to note that Poe's essay is often debated, and some critics argue that it's more of a literary game than a true account of his writing process. However, it does offer valuable insights into his thought process and the artistic choices he made in crafting "The Raven."