Sorry it's taken me a while to get back to this. I meant to sooner but will wave my ENP badge here, thank you very much (my best Elvis impression)
Actually, Jung never said that. The "we use all eight functions" model was introduced by Berens, Beebe and other more recent authors.
I haven't read much of the original Jungian literature, in any depth, on the functions. I wanted to at least do that before I questioned the above. I realize now while I have the inclination, I simply won't have the time to do this before posting a response. Woe to my real life responsibilities that served as a strict reminder this week that they do take priority over fun pursuits.

So, I'll pass on this for now and post a request instead: If you have suggestions for reading material where I can explore functional processes better, do list them here. I'd be interested in gathering the resources and going over them carefully.
I find this discussion interesting because I think cognitive functions are where the action is, so to speak in MBTI theory. The ability or skill with which one is able to use one's functions (4/8/16/32 - whatever your belief on the matter), in my opinion, relates well to the enneagram health levels. This also provides the diversity with types that we see.
I'm curious as well, if you think people only use their top four then why did the authors present all eight at all in a certain order. What was the point of referring to the bottom four in any sequence?
Okay, let me be clear--nobody has any empirical evidence for any typology system, myself included. I'm arguing why I think this interpretation is most internally consistent and describes people's motivations most effectively. Everyone's interpretation of something this amorphous is obviously subjective; typology is just a form of philosophy, not science.
Yes and we disagree on the thesis and the explanation for it. If the topic is that subjective then we could potentially have several different explanations regarding the internal processes which could all theoretically hold since they are dependent on the subject. By saying that there is one internally consistent or effective explanation, you imply it is an objective topic (any time this decision/thesis is made by someone on the outside, by definition). You're doing the same above and my point was that this is not consistent with the idea of a subjective topic.
I won't say it's totally impossible that such a shift could happen more than once, but it's not a voluntary or controllable reaction, and it's certainly something that would happen very rarely. It'd be like a religious conversion--some kind of huge revelation via profound life experience would have to convince you that the entire basis for your worldview has been completely wrong all along. This could theoretically happen to someone more than once throughout life, but it certainly would not be a routine occurrence and this still wouldn't allow people to use Fi/Te without completely getting rid of Ti/Fe's influence (or vice versa.)
Frankly, this is the hardest part to agree with as it implies mature folks who say they experience functions from their lower eight as per their type would necessarily have to get rid of their original preferences which have been honed, practiced and formed a basis or foundation for their behavior and worldview. This is the part that is least compelling.
I would like to know what leads you to believe that people use all eight attitudes routinely, then.
I think we have some miscommunication here. I don't, by any means, think people can easily tap into and use all their eight functions routinely. I think that would take away the usefulness of the types altogether. I agree that we have a preference ordering that is inherent to our type leading to a hierarchy of eight. These functions, the top four reflect the order in which we approach the world and when the top four are well-developed we see a healthy individual who may best reflect the stereotypical behavior of their type. However, being products of our environments as much as our internal cognitive processes, I think people may build different skill sets and develop different functions because of their environment. A Ti dom/aux with parents who are Fi dom/aux may in a positive environment be encouraged to develop that internal process not just the external manifestation. I think it can happen. As a function of our types, we are naturally more skilled and have greater access to our top 4 but life experiences and demands may encourage people to develop the lower eight with some or great difficulty.
But this is just a question of semantics regarding our definitions of Fi. I would define these "alien experiences" as manifestations of Fe, but obviously we're not going to agree on that. I don't think "I felt something emotional that was unfamiliar" is necessarily Fi, because I don't think the Ti dom in question is fully aware of where these feelings are coming from. For all we know, they might be validated externally even if the Ti dom doesn't realize it.
You seem to be listening to these experiences and deciding that they constitute Fi, without really knowing where the feelings came from or what the root cause of them was.
I'd rather people shared their own experiences than my posting and highlighting someone else's which they may or may not want highlighted in this context, which is why I was hoping we would have some Ti doms/auxs share their experiences and their own interpretation of those here as being Fi or not.
Listen, I'm not arguing that our brains are biologically incapable of using the shadow functions--just that switching to them requires permanently changing into a different personality type via some sort of life-changing experience. It's a dramatic shift in perspective that would edge out our old perspective....
So if I go along living my life and get to the point where I realize Fi actually makes more sense to me than Ti, then Ti has been pushed out of my functional makeup. If I reach a point where Fi truly resonates more clearly with my perspective than Ti, then Ti is gone--I'm not going to just switch between the two whenever I feel like it. The difference between Ti and Fi is that profound. If this happened to me, I would become an ENFP, which is possible but not something that would happen overnight or whenever I feel like it. And changing back to ENTP would require some equally powerful experience to convince me to rebuild my worldview again.
So when I say we don't use all eight functions, I mean we have a mold of four that makes up our worldview and that our worldview has to change profoundly and significantly in a way that clearly contradicts our old worldview in order to move into using the other four--and that once this happens (barring a similar revelatory experience in the other direction) there's no going back. The people I'm taking issue with are the ones who say things like, "Yesterday I used Fi for this and that, and today I'm using Ti for something else! Later this afternoon I'll use Fi again, but then I might use Ti tonight!" That's not how this works.
So my theory is that we're holding four tools at a time. At some point we may eventually decide to set down two (or even all four) of them and pick up some other ones, but this would be a very gradual and life-changing decision, not something people do on a daily basis. Picking up new tools requires setting other contradictory tools down--we can't hold all eight at once.
Again, this is not what I or most other posters here have said. Most of us acknowledge that we have a certain preference ordering and the shifts between them require a lot of work and a great deal of discomfort. I don't think we disagree here. I disagree that on the scale - that it would require a complete breakdown and rebuilding to be able to use one of the lower functions even weakly. I also don't agree that an ENFP can turn into an ENTP or vice versa. No. We don't choose our cognitive functions or type - these are innate. We can't choose our type as much as we'd like and even with life altering circumstances. We can however choose to work on honing or tapping into weaker functions as we find them to be more useful with age.
On the very last part about contradictory functions, it makes sense that we couldn't use Ti and Fi simultaneously in the same context. That is absurd. I think the disagreement is on the subject that you're suggesting these couldn't be used by the same user at all without completely abandoning the other in all contexts and life experience from there on and I think that is extreme. They could be utilized in different spheres with practice although always accompanied by some discomfort.
I believe that this theory is more representative of Jung's original model (which never actually says that any one person uses all eight functions routinely.) I'll continue to support this theory in my functional discussions until such a time as I change my mind.
Maybe later I'll end up deciding that we do use all eight functions--but that won't mean that I was a four-function believer and an eight-function believer at the same time, or that I had "access" to believing the eight-function theory before changing my mind. The point is, the four-function theory and eight-function theory cannot simultaneously be true, so I can't believe one without rejecting the other first--Ti and Fi share this relationship.
To continue the religious conversion parallel, I could be an atheist at one point in my life and later become a theist, but I'd have to discard atheism first and I would not routinely waffle between atheism and theism because these are really fundamental parts of one's worldview that simply don't change that easily. I see cognitive functions the same way--it's possible for an Fi/Te user to become a Ti/Fe user, but not without discarding Fi/Te first.
The religious parallel does not work because religion is ultimately a choice whereas cognitive functions - the hierarchy of these functions we inherit or is innate to our psychological makeup is not a choice we make for ourselves . Having said that, the disagreement is more about whether people use only four at any given point of time (a clear dichotomy) or whether they have access to using the weaker functions too (not simultaneously but not requiring a life altering experience either).
Digression on the subject of dichotomy in a religious context:
People do, in fact, change their religious beliefs, denominations, faith in a higher being -- all of it and for some, more than once.
Also, religion itself is far more complicated than the dichotomy expressed above. The way people approach their religion is also complicated. Being a theist or atheist is simply one choice, to make that leap of faith or not. People adopt one or the other as an identity but below that lies a far more complicated approach to their beliefs and motivations based on those beliefs. People, in practice adopt all sorts of weird combinations of beliefs and behavior that may or may not fit the simple choice of label. Some religious folks believe that humans have great and final agency in deciding their future which takes away from the complete faith in a higher being. Some atheists believe in less agency for humans while pointing to luck or a draw of cards as playing a large role in a person's life and experiences. It's all fascinating and more complicated than a simple dichotomy. There are also people who separate religious beliefs in a personal context from behaving in ways that would imply atheist leanings in other contexts. All that to say that this clear dichotomy does not even exist in this realm of clear choice.
I wanted to take the time to clarify the point about using these functions simultaneously and with great ease, flipping between them, as I do not hold that opinion. I do, however think these seemingly contradictory functions can be used by the same user at different levels of skill at different times during their life.
I think it would be fair to end with agreeing to disagree on this subject. I know better where you're coming from and will keep that in mind in future discussions of the topic. Thanks for playing!
