[31337Logic]

> If Mary knows everything about red then she also knows what seeing it is like.

Not necessarily. And if you assert it is true, then it can be true only in a limited sense.

Can you "know everything" about playing guitar if you've never actually done it yourself? I think you'll agree with me when I say the answer varies:

It's "Yes", if you mean "know everything" to stand for something like "know everything objective that can be passed along to another person without any loss whatever." (I'm thinking of things like how guitars are made, how they're tuned, how you play them, etc.)

But it's "No" if you mean "know everything" to also include your subjective first person experience of actually playing a real guitar (and why wouldn't you include that as part of your "know everything"?) If the subjective feeling is something to be known, then it ought to be included as part of your "know everything" list, right? (If not, why not?)