Maverick has a nicely observed post here on the different senses of 'I do not understand', as used by philosophers. For the sake of completeness I have copied it here.
CJFW was fond of use (i). If he said 'I do not understand' you knew that something very bad was coming your way. I'm not immune to it. And as a brief ad hominem can I point out the Peter Lupu is not immune to it either – I've lost count of the times he has said it, usually in sense (ii).
On this one, I genuinely don't understand what a truthmaker is. Its broad definition is: something that causes a truthbearer (a 'proposition') to be true. Part of my difficulty is with 'truthbearer'. What sort of thing is it? Is it a mental item like a thought? Is it a physical item of some kind? Or is it a Platonic abstract object? I'll assume the latter.
And what sort of causal relation obtains between truthmaker and truthbearer. Bill has said that it is not a cause that is mediated by some physical event or state, in the way that the sun rising is the cause of truth of the proposition 'it is day'. The truthmakerist holds there is something 'in between' the sun rising and the truth of the proposition, and this 'in betweenie' is being-day-ness or something like that. Is that right?
So there is supposedly some direct, unmediated causal relation between a physical item (the state of affairs 'being day') and an an abstract Platonic entity. And I am finding that difficult to get my head round, in sense (iii).
I also have the difficulty with future tensed statements like 'the sun will rise tomorrow'. Does that proposition exist as a truthbearer now, or tomorrow? Does its truthmaker exist now or tomorrow? I commented on that problem here. If the truthmaker for a future tensed proposition exists now, it seems difficult to avoid logical determinism. But if it exists in the future, we have to explain its coming-into-existence. Is the coming-into-existence or actual-existence part of the state of affairs that constitutes the truthmaker? Then it seems difficult to avoid the infinite regress problem I already pointed out.
And at this point my head is swimming with such difficulties and confusions that I can only confess misunderstanding in sense (iii) alone.