Arcadia Lesson Plan

What does Valentine mean when he says that the technique that Thomasina is using in her lesson book "hasn't been around for much long than...twenty years"?

Valentine means that the technique had not been "discovered" until recently, but Thomasina's notebooks reveal that she in fact discovered the technique in 1809. This hearkens back to Septimus's speech from Scene Three, in which he talks about human knowledge being gained and lost and then rediscovered over the years. Although Valentine cannot quite accept it, Hannah and he are discovering that Thomasina, despite her young age, was in fact a visionary genius.

As Valentine explains it, what is the nature of the...