To tell you the truth, i am more in favor of calling them modes, except now that i am in a relationship with someone who actually pays attention, i am told that i am not remembering things i said, did, heard in other modes. most frustrating. i did not start calling myself a multiple until a woman involved with jack accused him of having other people inside him. at that point we reluctantly re-considered the possibility. we had considered it years before but discarded it as we had only a few instances of memory lapse.
i have a theory that everyone has modes and that due to things like extreme stress, the modes can become more fragmented. i think this happened when we lost a job and could not figure out what was going wrong and couldn't fix it, even after asking.
but yes, mostly one at a time. sometimes i can watch , but there is only one mode i can do that with. there is another mode that sometimes influences me - not quite sure how that works.
most of my life i called them modes and when we talked i would tell people who overheard that i was talking to myself.
i am still figuring out how it works.