Hi! This is a blog looking at introjection, projection and introjects as a whole. Welcome!
To start us off, I want to explain first what introjection actually is! I think a lot of people forget what it means and what it refers to. So, in terms of psychology, introjection (or internalization) is an unconscious process. It's the process of internalising the thoughts or personality traits of others. It can be a normal part of a child's development, like when a child takes on parental values, attitudes, ideology, and such.
Introjection also works as a defence mechanism! They take the ideas, feelings, and/or attitudes of others and make that part of themself. Though it can be healthy, it can also be unhealthy; many may internalise negative or harmful beliefs. Introjection affects people's thoughts, too.
Introjection does not only apply to Dissociative Disorders! It's a process anyone can go through.
I see a lot of people talk about introjection online through the lens of introject alters, some I've seen have made it out as if only alter systems experience introjection; that's not quite right! While yes, introjects of people in our lives can exist, that's not all there is to introjection. It's not exclusive to CDDs.
Introjection is not the same as projection. While introjection is internalising those values, projection is where someone takes those internal beliefs and values and projects them onto external subjects. Projection can be a defense mechanism; used to expel and externalise those uncomfortable inner thoughts and feelings. Introjection is the opposite of projection.
Introjects are alters that hold onto those beliefs and values.
If they didn't introject those aspects, they wouldn't be considered introjects! Whether that be fictional or factual introjects, they need something to introject in order to be considered such. They need to have those compartmentalised aspects.
https://en.wikipedia.org/wiki/Introjection
https://www.simplypsychology.org/introjection-defense-mechanism.html
https://www.therapytrainings.com/pages/blog/introjection-understanding-and-addressing-internalized-beliefs-in-therapy?srsltid=AfmBOor_G-r3tS3fxMg-DMAoUJ-QCTKvN7mLbd2jOZMmJQ7cpSFP7Kod
https://changingminds.org/disciplines/psychoanalysis/concepts/projection_introjection.htm
https://www.goodtherapy.org/blog/psychpedia/introjection
https://www.sciencedirect.com/topics/medicine-and-dentistry/introjection