[Text taken from Chapter 11 of Carl Gustav Jung’s Psychological Types, first published in 1921.]
1. Abstraction, as the word already implies, is the drawing out or isolation of a content ( e.g . a meaning or general character, etc.) from a connection, containing other elements, whose combination as a totality is something unique or individual, and therefore inaccessible to comparison. Singularity, uniqueness, and incomparability are obstacles to cognition, hence to the cognitive tendency the remaining elements, though felt to be essentially bound up with the content, must appear irrelevant.
Abstraction, therefore, is that form of mental activity which releases the essential content or fact from its connection with irrelevant elements ; it distinguishes it from them, or, in other words, differentiates it. (v. Differentiation). In its wider sense, everything is abstract that is separated from its connection with non-appertaining elements.
Abstraction is an activity belonging to psychological functions in general. There is a thinking which abstracts, just as there is abstracting feeling , sensation, and intuition (v. these concepts). Abstracting – thinking brings into relief a content that is distinguished from other irrelevant elements by its intellectual, logical qualities. Abstracting-feeling does the same with a content characterized by feeling; similarly with sensation and intuition. Hence, not only are there abstract thoughts but also abstract feelings, which latter are defined by Sully as intellectual, aesthetic, and moral  . Nahlowsky adds the religious feeling to these. Abstract feelings would, in my view, correspond with the ‘higher’ or ‘ideal’ feelings of Nahlowsky  , I put abstract feelings on the same line as abstract thoughts. Abstract sensation would be aesthetic as distinguished from sensual sensation ( v . Sensation), and abstract intuition would be symbolical as opposed to phantastical intuition, (v. Phantasy, and Intuition).
In this work, the concept of abstraction is linked up with the idea of the psycho-energic process involved in it. When I assume an abstracting attitude towards an object, I do not let the object affect me in its totality, but I distinguish a portion of it from its connections, at the same time excluding the irrelevant parts. My purpose is to rid myself of the object as a single and unique whole, and to extract only a portion of it. Awareness of the whole undoubtedly takes place, but I do not plunge myself into this awareness ; my interest does not flow out into the totality, but withdraws itself from the object as a whole, bringing the abstracted portion into myself, i.e into my conceptual world, which is already prepared or constellated for the purpose of abstracting a part of the object. (It is only by virtue of a subjective constellation of concepts that I possess the power of abstracting from the object). ‘Interest’ I conceive as that energy = libido (v. Libido), which I bestow upon the object as value, or which the object draws from me, even maybe against my will or unknown to myself. I visualize the abstracting process, therefore, as a withdrawal of libido from the object, or as a backflow of value from the object to asubjective, abstract content Thus, for me, abstraction has the meaning of an energic depreciation of the object. In other words, abstraction can be expressed as an introverting libido-movement.
I call an attitude (v. Attitude) abstracting when it is both introverting and at the same time assimilates to already prepared abstract contents in the subject a certain essential portion of the object The more abstract a content, the more unrepresentable it is, I adhere to Kant’s view, which maintains that a concept is the more abstract, “the more it excludes the differences of things ”  , in the sense that abstraction at its highest level is absolutely removed from the object, thereby attaining the extreme limit of unrepresentability. It is this abstraction which I term the idea (v. Idea). Conversely, an abstraction that still possesses representability or obviousness is a concrete (v. Concretism) concept.
Notes by Jung
 Sully, The Human Mind , vol. ii, ch. 16.
 Nahlowsky, Das GefUhlsleben, p. 48.
 Kant. Logic, $ 6.