From its start in the early 18th century, the novel as a genre has always resisted easy definition. Samuel Johnson, literary critic and author of the first comprehensive English dictionary (check out a cool digital version here), defined the novel in 1755 as "a small tale, generally of love."
Johnson was probably thinking of early French romances in prose, which in turn likely developed from folk tales and ballads. But novels in English had already moved on, even -- or perhaps especially -- when their authors were not yet calling them novels. Henry Fielding, in the preface to his rollicking The History of the Adventures of Joseph Andrews (1742), calls his book a "comic Epic-Poem in Prose," a purposefully paradoxical definition that conveys Fielding's sense of humor, as well as his awareness of the genre's capaciousness, but does little to clarify what a novel should do or concern itself with.
Ironically, it was Fielding's rival Tobias Smollett -- whose own fictional works are now largely forgotten, at least outside academia -- who in 1753 came up with a definition of the novel much closer to our own:
A novel is a large diffused picture, comprehending the characters of life, disposed in different groups, and exhibited in various attitudes, for the purposes of an uniform plan, and general occurrence, to which every individual figure is subservient. But this plan cannot be executed with propriety, probability, or success, without a principal personage to attract the attention, unite the incidents, unwind the clue of the labyrinth, and at last close the scene, by virtue of his own importance.
In short order, Smollett strikes many of the notes that today's novels still strive to hit: a compelling main character, a broad or at least comprehensively imagined setting, and a compelling, satisfying plot.
The 18th century saw a profusion of types of prose fiction: epistolary novels (written in letters), it-narratives (written from the points of view of specific things, e.g. a carriage), early science fiction and fantasy (e.g. Jonathan Swift's still-entertaining Gulliver's Travels ), and so on. But for modern purposes, the novel owes its two main branches to a pair of authors writing in the early 19th century. One is still widely read -- in fact, she is more popular now than in her own lifetime! I refer, of course, to Jane Austen, whose intimate, sophisticated, somewhat ironic portraits of middle-class life in central England pioneer one of the hallmarks of the novel: psychological realism. In addition, Austen's novels of everyday life and modern courtship set the mold for every romance novel to come: girl meets boy, girl fights with boy, girl and boy make up and get married.
The other author to set the novel's modern parameters was Sir Walter Scott. By creating fictional protagonists and then placing them into real past events, Scott perfected the historical novel, which established social realism as the modern novel's other main hallmark. His series of Waverley Novels also instituted the model for all the long-running adventure and fantasy fiction series that now dominate the marketplace for books. (Perhaps you've heard of The Lord of the Rings? Or the Game of Thrones books? Or that little series featuring someone named Harry Potter?)
But the dual influences of Austen and Scott extend well beyond genre fiction. Let's consider two contemporary novels, each of which struck me when I read it as inheriting some elements from both "plain Jane" and Sir Walter. In Donna Tartt's much-lauded The Goldfinch (2013), winner of the Pulitzer Prize, a young man experiences tragedy early and then moves through a series of far-flung adventures while clinging to his titular prize possession. Tartt's novel has a plot that Scott would have recognized, I think, from his own tales of young men growing up in tumultuous times, along with a degree of sympathy for her main character's unrequited passion that Austen would have understood.
On the flip side, with a quieter tone as well as reception, Jesse Ball's no-less-accomplished recent novel Silence Once Begun (2014) sets down the author's fictional interviews with a series of Japanese men and women as he tries to figure out why an ordinary young man confessed to a series of crimes he did not commit and then took a vow of silence. Ball's searching psychological realism owes something to Austen; his use of a series of real disappearances in 1970s Japan as the inspiration for his plot clearly owes something else to Scott.
How much do we in turn owe to both Austen and Scott, as well as their many predecessors and contemporary inheritors? Nothing less than both the methods and the means by which we continue to tell stories about ourselves, and thereby continue to reflect on and shape our futures and well as our pasts and presents.