Arcadia asks some big questions about truth: does it even exist? What gives us grounds for thinking something is true? Is reason the right way to go about seeking truth, or is it better to trust your gut instinct? Arcadia's double storyline, alternating between modern-day researchers and characters in the historical period they're trying to discover the truth about, allows us to see where and how the contemporary truth-seeking process disintegrates – and it's not always where you'd expect. In Arcadia, the "plain and simple truth" is rarely plain and never simple.
Hannah's hunch that Septimus is the hermit appears to be true, while Bernard's stubborn conviction that Byron shot Chater is false. The play uses this contrast to suggest that valuing logic in general makes a person's guesses more likely to be correct.
Through focusing on proving that Bernard's theory about Byron is wrong rather than on proving that any theory is right, Arcadia suggests that the process of seeking for truth is really about looking for falsehood.