I don't think my AH does it on purpose. It is all to protect his identity to himself and to me.
I had a series of wake-up calls related to ex's gaslighting, first I doubted my own recall of situations, wrote a lot of stuff down to convince myself that I was right in my recollections of what did/didn't happen, then I realised that my recollectionsweren't faulty, (which was a relief) but I assumed that his reactions were due to being pickled - his memory was shot and the reason he changed tack or presented opposite sides of an argument as his long-held beliefs was that he was confused and his brain didn't work properly (because he was drunk so often), then I realised through a series of conversations I witnessed with other people (where I wasn't involved) that actually, he changed tack when he was losing an argument, incontrovertable evidence was presented to him for example, and I attributted this to him feeling attacked, people getting to close to attacking his sense of self, that this wasn't "on purpose", it was a defense mechanism.
my next big aha moment was this: "on purpose" doesn't equal "consciously". My ex was doing this on purpose, to deflect attention away from his short-comings, to make me or others doubt their own sanity in order to protect his self-image (which is frankly monstrous), it wasn't conscious, it was a defence mechanism, but it was on purpose, his brain purposefully deployed these tactics in a cycling output until hitting the best one for the situation at hand, because he had
learned that they worked. this might be a subconscious strategy, but it was, none-the-less, done ON PURPOSE.
This was a major wake up call for me, abusers aren't like they are depicted on TV, where they are alternately nice and nasty, but you can clearly see a conscious thought pattern occurring throughout it all: "I am going to do X to make her feel Y so that I can Z", abusers wrap a tight and complex layered web around their actions and thought processes and motivations, that most importantly sheild their own conscious mind from their true motivations and behaviour, it is nearly all subconscious but nearly all on purpose. Abusers don't view what they are doing as abusive.