Are you sure it's not false memory tho?
What does 'false memory' even mean, Ismene? Its unclear whether or not someone can actually have a false memory; or rather, whether the acceptance of this phrase indicates that all memories are false.
A memory is nothing more than a sequential ordering of neurochemical releases/activations/neuronal bonds (i.e. it is identical to the physical brain state that necessitates the possession of said memory).
I gather what you mean by false memory is something along the lines of a memory that does not
refer to an actual event in the (one's personal) past. In that case, I would say a large percentage of everyone's memories are 'false' insofar as it appears to be an innate capacity of the human mind to construct one's memories in such a way so as to incorporate more than the given physical (perceptual) stimuli (this would fall under the headings of imagination, fantasy, deeply ingrained biases, etc).
Actually, I'm fairly certain that if you could show that one's imaginations, fantasies, etc are causal effects of the perceptual stimuli, then ipso facto, the incorporation of this into one's memories would not necessitate a truth value of false.
You would also have to prove that one's memories actually
refer to anything at all, rather than being simply (i.e. VERY complex) brain states (the burden of proof is on the person whose argument is contingent on showing that memories refer to actual past events, I don't think they do).
In addition, you must be aware of the streamlining of consciousness (in that one's perception never takes in all stimuli, but rather discriminates against 'unnecessary' stimuli). In that case one never has a complete memory of ANY event. If something is incomplete does that mean it is false? I could surely imagine a counterfactual to support this (at least for some instances of memories). For instance, if a person drew two cards from a deck and placed them in front of you, and you only noticed (remembered) that she drew one card, and further told me that she only drew one card, we would be inclined to say that your memory is incomplete and false, or at the best, very misleading.
There is another way, I think, to defeat the usage of 'false memories' that involves the logical operation of disjunctions, but I will let THAT sleeping dog lie.
If psychedelics have shown me anything, I have become aware of how thin the line between so called 'reality' and the dynamics of my inner mind is.
And, finally, a popular philosophical thought experiment: how can we know whether or not we are actually brains in a vat?