nothing is but what is not

[aiyu]

Hi! This is from Macbeth:

Present fears / Are less than horrible imaginings:
My thought, whose murder yet is but fantastical, /Shakes so my single state of man that function
Is smother'd in surmise, and nothing is / But what is not.

Here, I doubt what 'nothing is but what is not' exactly means.
Does it mean 'what I see is only nothing'?

Thanks for your help in advance.

 

[lucas-sp]

Literally it means "the only things that exist [for me] are things that do not exist." Macbeth can't think about reality at this point - all he can think about is what might happen, what he might​ do.

 

[aiyu]

Many thanks, lucas-sp!