Both thinkers can be seen as Romantic for a couple of reasons. Both writers feature a very non- conformist view of the social setting. In fact, both writers spend much of their thematic development in trying to establish emotional frames of individuals who are apart from this conformist social setting. Hawthorne's conception of Puritan social norms in The Scarlet Letter as well as his critique of social hypocrisy would help to advance this. At the same time, Poe's exploration of the more frightening notions of self in his works and his poetry do so apart from the traditional concept of society. This would help to create a definite theme of Romanticism in their work. Combined with this overriding emphasis on emotions, both writers can be seen as examples of Romanticism in American Literature.
Other features of romantic writers include very descriptive writing, a focus on the supernatural or unexplained events, a belief in good verses evil, and a focus on aspects of human nature. Hawthorne is typically tied to the romantic period, and Poe is usually associated with the American Gothic period, which was an offshoot of the romantic period of writing. Romantics did focus on human nature and their relationship with God, often, and Gothics also focused on human nature, but tended to delve into the dark side of human nature. Poe's characters are often quite evil, insane or creepy in one way or another; he explores, in depth, the darker side of our souls and their capacity for evil.
Both authors use supernatural elements in their stories; for example, Poe has dead men's heartbeats, ghost cats, glowing bugs, and life after death and Hawthorne uses the events in the skies, the forest, and glowing letters in his stories. Both authors were very descriptive, and often had themes of good verses evil, and man's struggle with morality. All of these traits made Poe and Hawthorne romantic writers. Good luck!
It is a fact that people are influenced by their environment in which they live; if certain elements of this environment are in accord with what their natural predispositions are, people will embrace the influence of these elements and thinking. However, if these attitudes and ideals are the antithesis of their thinking, then a new movement of thinking usually commences.
Because Hawthorne's and Poe's view of the world was profoundly opposed to the optimistic views of their predecesors, Thoreau and Emerson and their followers, became what is referred to as the Dark Romantics. Nevertheless, they were affected by the environment of the Transcendentalists because they valued intuition over logic and reason. Both groups also saw signs and symbols in human events. In fact, the Dark Romantics employ the literary technique of symbolism to great effect. For instance, Hawthorne's "The Scarlet Letter" is replete with profound symbols, such as the letter and little Pearl. And, Poe, of course used cats, ravens, houses, the Red Death, and many other forces as symbolic.
While the Dark Romantics such as Hawthorne and Poe and Melville did not disagree with Emerson's belief that spiritual facts lie behind the appearances of nature, they did disagree that these facts must be necessarily good, or harmless. Hawthorne, for instance, suggests in his writing that Emerson merely takes the ecstatic, mystical elements of Puritan thought, ignoring the darker side--the Calvinistic sense of innate depravity of human nature, and the also Calvinistic notions of predestination. Hawthorne's perspective in his works is on both the mystical and the melancholy aspects of Puritanism and its thought.
In Hawthorne's and Poe's work, there is an exploration of the darker side and its conflict with good, the psychological effects of guilt and sin, and even madness and derangement in the human psyche. Behind what Herman Melville has called the "pasteboard masks" of social respectability, the Dark Romantics see the blankness and the horror of evil, a couterpoint to the optimism of the Transcendentalists.
To me, the thing that makes these two romantics is what they write about and how they write about it.
One of the themes of Romanticism is emotion and feeling. You can see this quite a bit in both men's work. Poe's work, especially, is highly emotional -- think about "The Tell-Tale Heart" or "The Raven." Similarly, the "Scarlet Letter" is very emotional as well.
Romantics are also really into the idea of dreams and visions. Again, you can see this quite clearly in Poe. Many of his characters seem to be experiencing these things.