Dr. Richard Schwartz, who founded IFS, thought of the mind as an inner family of multiple inner "parts," or sub-personalities, that are all good, but as we go through life and experience trauma and attachment injuries, they shift from their naturally valuable states into roles that sometimes can be quite distructive to us. They were in roles that were necessary when you were in the middle of experiencing trauma or a toxic parent. However, they get frozen into that time and believing that they still have to do this for you. Often, these "parts" don't know how old you are.
In IFS therapy, techniques that are usually used in family therapy are applied to help the inner system of the individual to heal by accessing and loving their protective and wounded inner "parts" with the goal of transforming them back to their naturally valuable state through releasing their burden.
Another key concept in IFS is that we are all born with the Self. It does not develop through stages or borrow strength or wisdom from others and it cannot be damaged. However, it can be overwhelmed or occluded by "parts."
When polarized "parts" blend, we live in the midst of an ongoing debate and have no peace of mind. However, when "parts" un-blend, the Self is immediately present and available. When the Self accepts and loves each "part", like a child who is terrorized into submission or an angry teenager who is exiled for standing up to persecution, the "parts" transform back into who they were meant to be.
It is the belief in IFS that our internal roles are not static and can changes with time and work. By recognizing that our inner "parts" contain valuable qualities and our core Self knows how to heal, allow us to become integrated and whole.
In essence, when "parts" are willing to differentiate, individuals feel centered, calm and light with a pervasive sense of well-being. And when the Self is differentiated from "parts" individuals experience what we call a "self-led state of mind" that is one of confidence and open-heartedness, where one feels a greater sense of choice and connection to others and the Universe.