Does Mary know I experience plus rather than quus?

Does Mary know I experience plus rather than quus?

by Phillip Goff

At first the demon thought this settled the matter. It seemed clear that, upon seeing the rose,Mary learnt something new: she learnt
what it’s like to see red . Before she left her black and white room Mary already knew all the physical facts about colour vision, so the new fact she learnt upon seeing the rose must be a non-physical fact about colour vision. Therefore, there are non-physical facts; therefore, physicalism is false. But soon the demon began to have his doubts.Perhaps, he thought, what Mary learnt when she saw the rose was just a matter of know how rather than knowledge that, or perhaps she learnt a new way of conceiving of a fact she had known already. Both of these hypotheses are consistent with physicalism.

‘What I need’, the demon thought, ‘is a new experiment, one that’ll settle the matter beyond doubt!’ The demon clicked his fingers, and, suddenly Mary appeared before him. ‘Right, young Mary’, said the demon, ‘I have a new mission for you. There is this young Welsh chap, Cuthbert,who lives in Aberystwyth. Your mission is to try to work out the nature of Cuthbert’s semantic phenomenology. Specifically I want you to try work out what Cuthbert’s perceptual experience represents ‘plus’ as meaning. Now I have a hunch that Cuthbert experiences “plus” to mean plus. But that’s just a hunch. I want you to work it out for yourself.