What do the words ‘yes’ and ‘no’ mean? Well, I can explain how their meanings add up. If I add the word ‘yes’ to the question ‘is it raining’ I get something with the same meaning as the assertion ‘it is raining’
“Is it raining? – yes” = ‘it is raining’
Similarly adding the word ‘no’ to the same question gives the corresponding denial:
“Is it raining? – no” = ‘it is not raining’
Does this shed any light on the question about negation and the principles of contradiction and excluded middle? I think so. For I suggested that one who questions either of these principles hasn’t really understood the meaning (or rather, the use) of words like ‘not’. Certainly, one who thinks that both ‘yes’ and ‘no’ are simultaneous replies to the same question, hasn’t understood the meaning of these interjections. For example, suppose someone utters ‘no’ then ‘yes’ in close succession.
“Is it raining? – no… yes” = ‘it is raining’
We would naturally take him or her to have changed their mind. I.e. At the time of uttering ‘no’ they were saying it was not raining, and then retracted it by uttering ‘yes’.
That deals with the principle of contradiction, namely is that it is impossible meaningfully to assert and deny the same thing. As for excluded middle, that follows from the fact that nothing else apart from ‘yes’ and ‘no’ counts as a reply to a question. Note that ‘not sure’ is not a relevant reply, for it is really the reply ‘no’ to the question ‘are you sure that it is raining?’, rather to the question 'is it raining?'. I.e.
"Is it raining? - not sure" = "are you sure it is raining? - no" = "I am not sure it is raining"
Failing to answer is failing to answer. Bullshitting is also failing to answer the question, but by means of asserting all sorts of other irrelevant things, or just outright nonsense.