The Progressive principle of “self” appears to be a “scientific” term. However, “science” pertains to the realm of actuality and the word “self”, as “the Progressive principle that binds soul to body” belongs to the realm of possibility.  “Social scientists” may treat their abstraction (of whatever the “self” means) as actuality, but this subtly changes the level of analysis from “maybe scientific” to “cryptotheological”.

My proof is by way of demonstration.

I can present the “self” in terms of an ancient Greek definition of “human” as “a soul bound to a body by way of spirit-descent”.

Here it is:  The “self” binds soul to body and establishes the person’s orientation towards “self-esteem”.