There's also a bipolar III, or used to be, where people only become hypomanic in response to medication, and other states that fall on the bipolar spectrum, like cyclothymia, where the person's mood only becomes slightly elevated or slightly depressed, but is still cyclical. I think "soft bipolar" is just a catchall phrase used to encompass bipolar-type mood fluctuations that don't fit the criteria for bipolar I or II, and are less serious, or less debilitating, than those dx's. That's what I got from reading, anyway.