1. Literary background
In Don Quixote (1605 & 1615) the knight lives out his own fiction by re-enacting fictions of chivalric romances. Following Cervantes' lead, Tristram, another fictional character, writes his own fictional autobiography in Tristram Shandy (1759-1767). Both books are metafictions: fictions about fiction. This is Sterne's 18th. century comment on reality, which is not something solid, but a construct of perceptions, narratives, fictions. The lesson for readers is that this applies, not only to Tristram's thoughts, but to their own thinking.
Applying the novel's traditional approach of characters over plot Richardson presented his narrative in realistic fashion by showing the momentary thoughts, feelings and gestures of his characters, who are more important than the plot.
Fielding's realism, on the other hand, followed the aristotelian design of plot over characters by focusing on the verisimilitude of his storyline and relying for credibility on probability.
Sterne found a way of bringing together both plot and characters by presenting Tristram as biographer of his autobiography, thus joining his character's perception from inside and outside.
However, what sets Sterne's narrative apart is that it parodies the new approach of the novel: formal realism. Tristram Shandy is a novel satirising the novel's pretended realism, just as Cervantes satired Don Quixote's knightly identity as a fantasy.
Tristram is the focus of Sterne's ironical characterisation. Trist(ram) is his name and defines his sad character. His novelistic identity is fused with his naming, yet his personal identity is a puzzle.
The passing of time in the novel depends, not on the clock, but on the narrator's stream-of-consciousness. This links Sterne's novel to Richardson's timing, which was expressed in the present tense in his characters' epistles. However, Tristram is also recounting his personal 'life and opinions' which allows him to adapt to a longer timeline, similar to Defoe's autobiography in Robinson Crusoe. Sterne also emulates Fielding's chronology, correlating his fiction with such family dates as those of Uncle Toby's battles in Flanders. Nevertheless, Tristram Shandy goes even further and presents a correspondence between literature and reality by offering the reader an hour's reading matter for every hour in his fictional life. This, of course, reduces the fictional realism of the novel to an absurdity since Tristram will employ more than an hour to pen an hour of his experiences: the more he writes the more the reader's time recedes.
Fielding organised his narrative sequences into scenes which counterpoint each other ironically. This occasionally appears overmanipulative on the author's part. Sterne, on the contrary, can manipulate all he wants without losing authenticity because his narrator is inside his own head and so unconcerned with external chronology. A chaotic narration is accepted by the reader since it is the reflection of the narrator's mental disorder.
Richardson's Clarissa has ideal goodness as a central theme. Sterne presents Uncle Toby in the same manner, as the embodiment of goodness. Fielding, of course, criticised Richardson's ideal as Shamela and Sterne, too, introduces an opposite to goodness: the villainous Widow Wadman.
Tristram Shandy owes much to Don Quixote's main characters who are dualistic representations of realism in Sancho and idealism in Don Quixote himself. Tristram's story also incarnates ideas and sensory input, but in one person. Sterne, following Cervantes, suggests that truth is neither completely external, as science would have it, nor only introspective, as humanism perceives it, but that reality is a collection of different narratives.
Richardson was distinguished from Fielding by their differing emphasis on the individual and the social. This double realism in the novel is later exemplified in French literature by Balzac's sociological emphasis on the exterior and Proust's psychological analysis Yet both are considered realists. Sterne synthesises both approaches since he explores both the inner and outer worlds from inside Tristram's head.
2. Philosophical background
The dualistic approaches to knowledge go back to the realism and idealism of platonic ideals and aristotelian pragmatism.
However, the Enlightenment emphasised this distinction further in Descartes' dualistic vision of inner and outer: "I think therefore I am." The philosophical problem led, logically, to the question of how the inner I could know the exterior world.
Novelists, however, though recognising the differences between interior and exterior have chosen to accept both as 'real' and focus on the problematic relationships between them. Defoe's memoir style is especially suited to displaying the tensions between inner and outer worlds. He uses the Cartesian individualistic view to define both the internal and external worlds more clearly. Later Proust also presented both the Third Republic and his personal introspective analysis.
Locke defined identity through memory of the past, which enables a continuity of self-awareness. Hume continued this theme when he analysed the development of personal identity as causation, the perception of previous cause and later effect which are not related in reality, only through perception. Sterne's Shandy is conscious of his own personality through the comparison of past and present experiences, but in the end is unsure of who he is.