What do you mean and how do you know it?
What do you think you know, and how do you think you know it?
How do I know that what I mean to say is true, or how do I know what it is that I really mean?
What do you mean and how do you know it?
What do you think you know, and how do you think you know it?
How do I know that what I mean to say is true, or how do I know what it is that I really mean?