And of course the idea that "no-one can really know anything" (Hume?) is self defeating because if we can't know anything then we can't know that we can't know anything.
This is an issue of language and semantics. I think the situation can be clarified by making a distinction between 'knowing' and 'being aware'. We can be aware that we don't really know anything, provided we define knowing as a complete understanding.
If we define 'knowing' in a partial and incomplete sense, which it has to be, because no-one has a complete understanding of anything, then it's clear that we can't know that we can't know, but perhaps we can be aware that we can't know, or be aware that we can't have a complete understanding of anything. In other words, if knowing is defined as a 'partial understanding', then knowing that we can't know anything, translates as having a partial understanding that we can't have a partial understanding of anything, which, I suggest, is not true.

There are lots of oddities in human language. One of my favourites, as an Australian, would be the following statement, "All Australians are liars". Since I'm an Australian, such a statement cannot be true, therefore the statement "All Australians are liars", must be a lie.
