A major dualism located within Western philosophy and theology is that between inner and outer. As it goes, there are two primary worlds, one that is exterior and one that is interior.
In Platonic metaphysics, that the West has primarily inherited through Augustine and Renaissance Neo-Platonism, the outer world is one of change and flux. Matter is ontologically inferior. It is either on the low scale of a chain of being, a defective product of a not wholly competent demiurge, or some ugly putty that the forms have pressed themselves into. The inner world is the world of the soul, the pure aether where the Forms can be recalled or sought after. The inner life can become corrupted by being in love with the outer, but when the soul is directed to its own image, it is saved. The soul is divine and is itself a reflection of the One, or has, in itself, knowledge of the Forms, the really Real. Ultimately, Platonic philosophy is to strongly demarcate the realms and pursue true knowledge.
Kantian metaphysics follows Plato in affirming the demarcation, but does so by overthrowing the metaphysical basis. Kant, in order to save Philosophy (which means Plato, "all of Western philosophy is but a footnote to Plato"), eradicated the metaphysics and postulated a synthetic a priori instead. We can't really know the realm of the Forms, or any kind of notion of the Real, but it's the only thing that makes sense of what we see. We cannot lean on Reason alone, as it will not provide the deep answers Philosophy seeks. Our reason cannot peer behind the surface, we can only see things-as-they-appear, and not things-in-themselves (phenomenal/noumenal). So we must start by assuming the existence of God, freedom, and the immortality of the soul. Only then will we be able to protect the inner life from the acid of Postivistic Science from completely eradicating the soul. This is the kind of horror that the novel 'Frankenstein' sought to address. Science might grasp all the mechanics of the outer world, but the inner world remains safe and real. This is the first necessary step towards Existential philosophy.
I want to question that demarcation between inner and outer, but not abandon the spirit of it. If I was to abandon it entirely, one has to affirm materialism and such is the absurd conclusion of Positivism. Life, consciousness, and the plethora of transcendentals cannot be made sense of in such a framework. Kant was right to begin his project in order to guard against the absurdity of the Enlightenment's mechanizing of Man.
Instead, I want to offer the idea that there is no inner or outer, and thus reality is truly on the surface. However, reality is also folded. Surface realities can be compounded upon one another to create folds within reality that are not perceptible to the outward searching of the eye. This is where the soul dwells. Like a dog under a sheet, we see movement, but we do not see an animal. The Greeks used to speak of the soul as being seen in the flash of the eye. There's some beautiful turns of phrase in Homer's poetry that convey this. We see life in the flicker in eyes, the twitch of the body, the graceful movements of the flesh. It's what separates life from a-life, and bios from zoon. In the former distinction, one sees a difference between a plant and a rock. In the latter distinction, there's a difference between the life of a beast and the life of a man. Reality possessed more folds from which things dwell.
Why does this matter?
Firstly, this corrective to Plato's revolutionary philosophy makes sense of the earthiness of the Biblical witness. The Scriptures clearly affirm the reality of the soul. Man is not merely a brute beast, but something else. I'm with the early Patristics that affirm the soul is the Image of God in Man. However, if we read this in terms of Platonic metaphysics then we will be misled to what this means. We ought to avoid the inner-outer distinction. Otherwise we denigrate the body, and the material world, as inferior or worthless. Instead, the soul is the folded reality of experienced life. The soul is infused in the body, a kind of aura that permeates. It's not merely nerve endings, or bio-chemical reactions. However, it is coexists in such forms. So, I feel pain and I act accordingly. I am a creature, like the other animals, but I am something else, made in the Image of God, destined to His likeness.
Secondly, this affirms the objectivity of Beauty. Particularly here I'm drawing on D.B. Hart's work. Beauty can be an objective reality if the soul's subjective experience is not a buffered off zone. Beauty is found within the folds. Of course, there's many angles of Beauty, but it's found in the complexities and intricacies of folded reality. This avoids subjective derangement into an aesthetic of "whatever". However, one must be careful not to imperialize this fact, and narrow the eye of the soul. This occurs when a culturally contingent metaphysical demand becomes a universal criteria. Participating in reality is enough to allow a plethora of experiences and developments of the soul. The soul becomes open to seeing the intricacy of folds and many meanings be opened or kept veiled.
Thirdly, this affirms some of the weird postulates modern science has offered. I'm not a physicist, but as I've heard, the firm line between matter and energy, particles and waves, is fuzzy. I've heard that all matter is really just energy. Weirdly enough, some early Christians affirmed the same (c.f. Gregory of Nyssa in 'On the Soul and the Resurrection'). Thus, a dualism of inner and outer begins to fade if this is in fact true.
Fourthly, this makes sense of a particular kind of theology of revelation. We cannot merely think in terms of discarding a husk of contingency and getting to the kernel of eternal truth. The garb truth wears is itself apart of the truth. Thus, the affirmation of the Incarnation is, in a sense, saying God has eternally said Yes to His redemption of Mankind, full-stop. Now, whenever we say God, we must think Jesus Christ. The garb the Eternal Word wore is now everlastingly present. The same is with the Bible. We must not read literalistically, vis. modernists or fundamentalists, nor can we read allegorically or existentially, vis. some Patristics or Bultmann. The history of the Bible is the garb God has chosen to wear in speaking to Man, and it's something that must be taken into account.
Fifthly, similarly, this alters our interpersonal ethics. Sometimes I think it'd be easier if I had superpowers like The Purple Man (c.f. Jessica Jones) whose commands are irresistible. If he asks someone to tell him the truth, they obey. However, what this power misses is the actual truth. The fact someone might lie, or hesitate, or tell the truth in a riddle, is itself apart of the truth. If someone never believes me, and I intentionally lie so that he does the opposite, and thus I indirectly tell him the truth, then this is itself apart of the reality of the situation. To maintain an inner and outer dimension ignores the mediating moment between thought and word.
Augustine maintains the same, but his inner/out distinction forces him to put lying into strictly metaphysical terms. Instead, this misses the larger point of the foldedness of the mind and the spoken word. The twists and turns of the body, in fact, reveal flashes of the soul. As per the above illustration, one might understand a dog's temperament by watching it squirm under a blanket, rather than merely tearing it off to the scrutiny of the curious eye. Lying is not unethical because the inner-life is a vestigia trinitatis. Lying is unethical because it's many times an assumption of the ability to command reality and forge it into your own image. You distort the folds of reality for your own purposes. However, the discerning eye can still see the truth in spite of a lie.
However, what this means is that in my relationship with people, I ought to respect their alterity. I am not trying to strip through whatever surface appearance and figure out their inner character. A lot of therapy, Christian and not, functionally does this to people. The therapist is the scientist watching some categorically different thing react to a procedure. Instead, we ought to learn discernment and watch the folds of a person's life and see how that tells us about who they are. The goal is not to take off the masks' people where. In fact, the mask they wear can tell a lot about the person underneath. Sometimes the mask is itself a form of communication when other means don't work. Exaggeration is shouting in a world that is mostly deaf (Flannery O'Connor).
All of this is not to say Plato is an idiot, or that Western theology, since Augustine, or even in the Kantian revolution, is bankrupt or worthless. But there's a way to move beyond and return to a better way of seeing things. Let's take what's good and move on in our journey towards the glory of God.