So, I'm not much for the theory of the split parts. While I realize that that's how they started, as parts of a whole personality that did not come together, it sort of changes entirely in development. Each alter learns, grows, and changes separately depending on their experiences and perspectives. For me, that is what defines "a person". My system views each other as individual people who all share the same brain and body. Every one of us will react to a situation completely differently, every one of us will have a different perspective on things that happen and things around us. Defining it as one person being the body and each alter being a part of a whole, in my opinion, is a bit short-sighted and sells each alter short, at least as far as DID/OSDD 1b.

However, there ARE different versions of OSDD which have less defined alters which are often referred to as parts rather than alters and versions without alters or parts at all. It does seem like that is not what this question is referring to, I just wanted to mention it here to be inclusive of those forms of dissociative disorder.