Although commonly called a novel, The Scarlet Letter is actually a romance. Hawthorne makes this distinction because at the time he was writing, novels were supposed to deal with realistic representations of human experiences or external truths. Romances, on the other hand, were concerned with internal truths, or "truths of the human heart," as Hawthorne states in his Preface to The House of the Seven Gables. Romances, therefore, allowed the author to deviate from reality in favor of imagination. Thus The Scarlet Letter is not an historical novel about Puritan Boston, but a romance set 200 years before Hawthorne's time in which he tells a tale that may have occurred, given some historical facts and many insights into human nature.
Writing a romance about the past gives Hawthorne the freedom to present several versions of what might have happened, depending on whose perspective is presented. This is why after the death of Arthur Dimmesdale, several theories are submitted as to how the scarlet "A" came to be imprinted on his breast. The insignia could have been self-inflicted, or wrought by Chillingworth's magic, or a manifestation of Dimmesdale's remorseful spirit. Hawthorne presents all three theories non-judgementally because what matters most is not how The Scarlet Letter got there, but that it confirms the truth about Dimmesdale's adulterous heart.
The genre of the romance also allowed Hawthorne to embellish the relationship between humans and nature. For example, the babbling brook in the forest scene appears to sympathize with Hester and Dimmesdale and adds "this other tale to the mystery with which its little heart was already overburdened ...." (p. 201). In addition, the "A"-shaped meteor which appears the night Governor Winthrop dies and Dimmesdale stands on the scaffold is interpreted as both a sign from heaven denouncing Dimmesdale as an adulterer and also as standing for "Angel" as the soul of a revered magistrate ascends into heaven, depending upon the orientation of its observer.