So you agree that A could exist but I imagined it?
What are our options then?
A exists and I have experienced A
A does not exist and I have not experienced A
A does not exist so I have not experienced A
B exists but I am mistaking it for A
A does not exist, B does not exist and you are suffering delusions...
A does not exist, B exists and is actively deceiving you...
A does not exist and your subconscious is actively deceiving you...
A does not exist and confirmation bias is leading you to mistake random events for a sensation of A...
1: How do we know A not to exist?
We don't know, but in the absence of evidence to support the claim we can dismiss it.
2: How can B be mistaken for A?
B can be deceptive. People are imperfect witnesses.
3: How is an experience an experience of A?
Who said that it was?
If it quacks like a duck it is a duck. Of course I could try, delusion or illusion if I were you
If it quacks like a duck it could be a duck, or a CGI simulation of a duck, or a model of a duck, or someone with a hearing impairment misunderstanding a goose, or a liar, or someone that really, really, really wants it to be a duck falling prey to confirmation bias in the presence of a swan, or someone stood close to a synthesiser loaded with the recording of a duck...
O.