I've not done any courses on psychology, but the subject greatly interests me and I've done a lot of research on my own time in to it. However, I'm not quite sure where to start looking with this particular problem.
I've known a few people that can change their mind on a subject that they can completely justify by using their own internal logic. However, that logic can be easilly deconstructed. There also tends to be a degree of revisionism in how they view certain subjects and what they thought of it at the time. It's not like something like borderline personality disorder where the changes tend to be rapid, these changes of mind tend to happen with at least a month's gap.
Where should I be looking to get a better idea of what this is classified as?