The language of Arcadia switches between the colloquialisms of early 19th century England and those of modern England. Stoppard's language reflects his periods, historical and modern, and he uses speech patterns and lexicons in keeping with his characters.
But his is a stylised dialogue, conveying the "look and feel" of the past as perceived by the modern audience. Still, it has sufficient latitude in register to make plain the relationships between the characters. For example, Septimus, after failing to deflect a question from Thomasina with a joke, bluntly explains to his pupil the nature of "carnal embrace" – but this bluntness is far removed from that with which he repudiates Chater's defence of his wife's honour (which he says "could not be adequately defended with a platoon of musketry"). With Lady Croom, who sees Mrs. Chater as a "harlot", Septimus delicately admits that "her passion is not as fixed" as one might wish.
In the modern sequences, the dialogue is more realistic. But Bernard consciously assumes some stylisation of language: He rehearses his public lecture in heightened, flamboyant rhetoric; and he unleashes a "performance art" polemic against Valentine's scientific thought, not from spite but for "recreation".
The play's scientific concepts are set forth primarily in the historical scenes, where Thomasina delivers her precocious (or even anachronistic) references to entropy, the deterministic universe and iterated equations in improvised, colloquial terms. In the modern era, Valentine explains the significance of Thomasina's rediscovered notebook with careful detail, reflecting Stoppard's research into his play's scientific materials.
Consciously echoed phrases, across the time frames, help to unify the play. For example, Chloe asks Valentine if "the future is all programmed like a computer", and whether she is the first to think that theory discredited "because of sex". Thomasina has been there before: "If you could stop every atom in its position and direction ... you could write the formula for all the future," she tells Septimus, then adds, "Am I the first person to have thought of this?" The difference is significant: Chloe's intuitive version allows for the effects of chaos, illustrating Stoppard's theme of the interdependence of science and art, and of professional and amateur thinking.