What This Concept Is About
To understand 內外空 (adhyātma-bahirdhā-śūnyatā, "emptiness of the inner and outer"), we must first set aside a mode of thinking that contemporary people fall into all too easily: splitting the world into "inner (my mind)" and "outer (the objective world)" as two independent entities.
In the fine-grained dissection of the Dharma, all our experience of life and the universe is, in essence, nothing but the collision and mutual dependence of the 六根 (ṣaḍ-indriya, six faculties; 内六入/内六处, adhyātma-āyatana, the six inner sense bases: eye, ear, nose, tongue, body, mind) and the 六尘 (ṣaḍ-viṣaya, six sense objects; 外六入/外六处, bahirdhā-āyatana, the six outer sense bases: form, sound, smell, taste, touch, mental objects). We are accustomed to establishing a solid "self" (subject) seated at the center of the mind, perceiving and manipulating the "not-self" object (the external world). And "emptiness of the inner and outer" is precisely the blade with which the Dharma dismantles this "inner-outer opposition" and "subject-object clinging" on the path of liberation.
To grasp "emptiness of the inner and outer" precisely, one must strictly distinguish its levels and connotations according to the classical scriptures, and must never crudely reduce it to a word-for-word gloss:
1. The Precise Structure of the Concept: Inner Emptiness, Outer Emptiness, and Emptiness of the Inner and Outer
- 内法/内六入 (inner emptiness): refers to the six perceptual organs and cognitive mechanisms: eye, ear, nose, tongue, body, mind. "Inner emptiness" here by no means refers to the withering of organs or the cessation of mental activity, but rather to the discovery, in true contemplation, that the inner six entrances are 无自性 (niḥsvabhāva, "without self-nature"), substanceless, not-self, not-mine, and not a deity (神, ātman). The eye cannot generate eye-consciousness by itself; the mind faculty has no fixed, unchanging substantial soul. - 外法/外六入 (outer emptiness): refers to the six kinds of objective perceptual objects: form (light, shadow, appearance), sound, smell, taste, touch (texture), and mental objects (abstract concepts and images cognized by consciousness). So-called "outer emptiness" does not mean that external physical matter does not exist or dissolves into nothingness, but that the outer six entrances have no self-nature that can exist independently apart from the perceptual system — they are non-aggregated, indestructible (not a substance that can be destroyed), and ungraspable. - 内外法 (emptiness of the inner and outer): that is, the entire network of subject-object experience woven from the interweaving of the inner six entrances and the outer six entrances. The core meaning of emptiness of the inner and outer is: when the inner six entrances and the outer six entrances meet in mutual dependence and give rise to experience — whether the subjective perceiver, the objective perceived object, or all the physiological, physical, and psychological phenomena at the boundary between the two — all lack an independently inherent substance (no self-nature); their nature is originally empty and still.
2. The Double Deconstruction in the Classical Scriptures: The Physio-Physical "Space Element" and the "Thusness of Nature" of Prajñāpāramitā
In the classical scriptures, the exposition of "emptiness of the inner and outer" displays a complete arc from shallow to deep, from contemplative practice to ultimate reality:
- **The physiological/physical contemplation in the Āgamas (taking the *Middle-Length Āgama* (《中阿含经》, Madhyama-āgama) as an example)**: In meditative practice, the *Middle-Length Āgama* specifically delimits the 「内空界」 (ādhyātmika-ākāśa-dhātu, "inner space element") as the apertures inside the body not covered by flesh, skin, bone, or sinew — such as the eye sockets, ear canals, nasal passages, mouth, the moving throat, and the digestive and excretory channels; while the 「外空界」 ("outer space element") is the physical apertures of external space. The practitioner must contemplate with wisdom, as it truly is: 「彼一切非我有，我非彼有，亦非神也」 (*"None of these are mine; I am not theirs; nor are they a deity"*), thereby causing the mind not to be defiled by attachment to the limitations of space and the body, and accomplishing the 「不放逸慧」 (*"wisdom of non-negligence"*) and the 「正知」 (samprajanya, "clear comprehension") within concentration. If, in meditative contemplation, one's mind is stirred and unsettled by 「念外空」 ("thinking of outer emptiness"), one instead turns to 「念内外空」 ("thinking of emptiness of the inner and outer"), and even to 「念不移动」 ("thinking of the immovable"), repeatedly softening and taming the mind, leading it toward clarity and liberation.
- **The Mahāyāna contemplation of ultimate reality in the Prajñā and *Great Collection* scriptures (taking the *Mahāprajñāpāramitā-sūtra* (《摩诃般若波罗蜜经》) and the *Mahāvaipulya-mahāsaṃnipāta-sūtra* (《大方等大集经》) as examples): The Mahāyāna scriptures place emptiness of the inner and outer at the head of the 十八空 (aṣṭādaśa-śūnyatā, "eighteen emptinesses"), further elevating its meaning. The Mahāyāna scriptures repeatedly emphasize: the empty, still nature of the inner and outer six entrances is 「非常非灭」** (*"neither eternal nor extinct"*), and its fundamental cause lies in 「诸法性尔」 (性自尔, dharmatā, *"the nature of all dharmas is thus"*) — that is, all dharmas are originally so; they are not empty because they were destroyed, nor have they changed from being into non-being. The scriptures describe emptiness of the inner and outer with 「非积聚、不可坏、不可取」 (*"non-aggregated, indestructible, ungraspable"*), pointing out that all dharmas originally have no self-nature or substance, and therefore cannot be disassembled or accumulated, nor can they be genuinely destroyed or grasped as entities.
Going one level deeper, prajñāpāramitā emphasizes 「空中无眼耳鼻舌身意，无色声香味触法」 (*"in emptiness there is no eye, ear, nose, tongue, body, or mind; no form, sound, smell, taste, touch, or mental object"*). If a practitioner deludedly tries to grasp a state or appearance of "emptiness of the inner and outer," attempting to make the "empty mark appear (emerge)," one is in fact attempting to make the 「无相法出」 (*"markless dharma emerge"*) — this itself is a subtle attachment. The true practice of prajñā is 「不不见色若相应若不相应」 (*"not not-seeing form, whether corresponding or not corresponding"*) — not only not clinging to external objects and the inner mind, but also not clinging to "emptiness" itself.
3. The Place of "Emptiness of the Inner and Outer" on the Path of Liberation
On the entire path of liberation, "emptiness of the inner and outer" is the pivotal point for breaking through the dualistic opposition of subject and object and the view of self-nature (svabhāva-dṛṣṭi).
Many practitioners can contemplate the impermanence of external objects (breaking outer dharmas), yet secretly retain a "contemplating inner self"; or they can contemplate the rise and fall of inner thoughts (breaking inner dharmas), yet treat the external environment as a real, oppressive source. "Emptiness of the inner and outer" sweeps up both "subjective cognition (inner)" and "objective environment (outer)" in one net, severing any foothold to which the afflictions 烦恼 (kleśa: craving 贪, aversion 瞋, delusion 痴) can attach. In the *Mahāvaipulya-mahāsaṃnipāta-sūtra*, the Buddha even explains 「内空、外空、内外空」 (inner emptiness, outer emptiness, emptiness of the inner and outer) as the foundation of the Tathāgata's unobstructed wisdom that knows all the realms of sentient beings, and as the first dharma-gate by which the practitioner, through the 空解脱门 (śūnyatā-vimokṣa-mukha, "emptiness liberation gate"), settles all sentient beings in the 无为界 (asaṃskṛta-dhātu, "unconditioned realm").
A Walkthrough in Everyday Life
So that "emptiness of the inner and outer" does not degenerate into an abstract term, let us use a scenario utterly familiar to contemporary people — "late at night, exhausted from overtime, scrolling your phone and seeing a peer who got rich and is on vacation" — and walk through this psychological process step by step according to the classical definitions, while pointing out where the mapping most easily goes wrong.
Step One: Walking Through the Inner Six Entrances (Inner Dharmas) — Breaking the "Experiencing Subject"
- Contemporary scenario: your eyes look at the screen (eye base), your ears listen to the video's music (ear base), your finger swipes the screen (body base), and in your mind arise anxiety, envy, and self-deprecation (mind base). - Common mis-mapping: we usually think: "I am looking, I am envious, my brain is tired." We attribute the operation of these inner six entrances to a fixed, unchanging "self/soul (deity)." - Classical doctrinal mapping (inner emptiness): contemplate the eye, ear, nose, tongue, body, and mind as they truly are. The eye faculty is merely a light-sensitive organ; the mind faculty is merely the basis on which thoughts arise. The arising of eye-consciousness (眼识, cakṣur-vijñāna) and mind-consciousness (意识, mano-vijñāna) depends entirely on neural signals and accumulated memories — among them there is not a single fixed "I" controlling or owning them. The inner six entrances are 「非我有，我非彼有，亦非神也」 (*"not mine, I am not theirs, nor are they a deity"*); the self-nature of inner dharmas is originally empty.
Step Two: Walking Through the Outer Six Entrances (Outer Dharmas) — Breaking the "Experienced Object"
- Contemporary scenario: the colors and light on the phone screen (form base), the blogger's triumphant laughter (sound base), the cold phone body in your hand and your fatigue (touch base), and the abstract concept in the screen that "others have it better than me" (mental-object base). - Common mis-mapping: we think the "successful world" in the screen is a real, hard-core entity that objectively oppresses me and deprives me of happiness. - Classical doctrinal mapping (outer emptiness): the light and shadow on the screen (form) are just pixels emitting light; the blogger's laughter (sound) is just air vibration. They are 「非积聚、不可坏、不可取」 (*"non-aggregated, indestructible, ungraspable"*). You cannot actually pull the luxury resort out of the screen; that so-called "successful world," apart from your cognitive system, has no self-nature that exists independently. The self-nature of outer dharmas is originally empty.
Step Three: The Contact of Inner and Outer (更乐/触, sparśa, "contact") and the Manifestation of "Emptiness of the Inner and Outer"
- Contemporary scenario: when the "tired eye (inner form)" meets the "harsh screen light (outer form)," and the "comparing consciousness (mind entrance)" meets the "concept of others' success (mental-object entrance)," the collision (classically rendered 更乐, i.e., 触, "contact") gives rise to an extremely unpleasant suffering feeling and envy. - Common mis-mapping: contemporary people often try to solve the problem by "changing the external environment" (turning off the phone, going shopping, making money) or "controlling the inner mind" (forcing oneself not to envy, staying positive). This is an endless struggle conducted on the premise that both inner and outer are real. - Classical doctrinal mapping (emptiness of the inner and outer): 1. Contemplation of the physiological/physical space element: realize that at this moment the saliva flowing in the mouth, the swallowing of the throat, the breath entering and leaving through the nasal and pulmonary passages (inner space element), and the flow of air in the room (outer space element) are essentially identical — both are the flow of the selfless 空界 (ākāśa-dhātu, "space element"). 2. Contemplation of ultimate reality: realize that the "envious inner mind (inner)" and the "envied external state (outer)" arise simultaneously in dependence on conditions. Without the external light, shadow, and concept, the inner envy could not arise; without the inner cognitive mechanism, the external light and shadow would be meaningless. Their interweaving is 「非常非灭，性自尔」 (*"neither eternal nor extinct; such is the nature"*). 3. The immovable mind and clear comprehension: when you no longer treat the "inner" as an injured self and no longer treat the "outer" as a real world that harms you, the mind is no longer dragged along by external states (「念内外空，心不移动」, *"thinking of emptiness of the inner and outer, the mind does not move"*). Anxiety and envy instantly lose the soil on which they depend, and dissolve like illusions. This is 正知 (samprajanya, "clear comprehension") and 心不染着 ("non-defilement of mind") in contemporary life.
Why Contemporary People Need It
Contemporary life is held hostage by a high degree of 「主客二元化」 (subject-object dualism) and 「信息过度刺激」 (information overstimulation). The unprecedented loneliness, anxiety, and mental attrition felt by contemporary people can often be traced to a two-fold reification of "inner" and "outer":
1. Dissolving "Self-Inflation" and "External Oppression" in the Algorithmic Age
Contemporary internet algorithms (recommendation systems, social media) are built on an extreme reinforcement of the "inner-outer opposition." Algorithms keep feeding content that matches your preferences, strengthening your "inner (self-preference)," while packaging the "outer (world)" into a series of stimuli. Contemporary people either fall into extreme individualism (thinking "I" am the center of the world and the external must obey me), or into extreme helplessness (thinking external housing prices, class, and workplace environments are like indestructible boulders crushing "me").
"Emptiness of the inner and outer" offers a thorough antidote: it tells you that the enormous structures outside that make you anxious are, in essence, 「非积聚、不可坏、不可取」 (*"non-aggregated, indestructible, ungraspable"*) — they have no inherent oppressive power independent of cognition; and that sensitive, fragile, perpetually wounded "you" — your inner six entrances are likewise 「非我有，我非彼有」 (*"not mine, I am not theirs"*). When the hard blocks at both ends of subject and object are dissolved by emptiness, the mental shackles fall away in an instant.
2. Comparison with and Transcendence of Contemporary Science (AI, Cognitive Neuroscience)
Contemporary cognitive science and the development of artificial intelligence provide an excellent analogy for understanding "emptiness of the inner and outer":
- Comparative analogy: in cognitive neuroscience and large language models (LLMs), so-called "perception" and "thought" are nothing but the complex interaction between input (sensors/data, analogous to the outer six entrances) and network weights/neuron activations (analogous to the inner six entrances). Science tells us that there is no little man (homunculus) in the brain controlling everything — which is remarkably similar to the Buddhist deconstruction of "a deity/self in the inner six entrances." - Limitations and open questions (must be stated): however, the scientific analogy is by no means equivalent to Buddhist emptiness. Contemporary brain science and AI research are still built on "materialist substantialism" or "functionalism"; they treat neurons, electrical signals, and data streams as objectively real physical components (still falling into "outer dharmas are real" or "accumulation is real"). More importantly, scientific research remains at the level of third-person, object-level description and cannot provide a first-person liberating experience. Science can tell you "there is no fixed self in the brain," but it cannot eliminate your despair when you are laid off; whereas the Buddhist "emptiness of the inner and outer" is a thorough realization in meditative contemplation (禅观), aimed at severing afflictions and attachments and leading to liberation in the unconditioned realm.
Common Misreadings and Clarifications
Misreading One: Understanding "Emptiness of the Inner and Outer" as "Both Inner and Outer Physically Do Not Exist (Nihilism / Annihilationism)"
- Clarification: this is the most widespread misreading, equating "emptiness" with "nonexistence." The scriptures clearly state that the essence of emptiness of the inner and outer is 「非常非灭，性自尔」 (*"neither eternal nor extinct; such is the nature"*). "Emptiness" does not mean that the eye, ear, nose, tongue, body, mind and form, sound, smell, taste, touch, mental objects physically vanish into thin air, nor does it mean that one must gouge out the eyes or plug the ears to be empty. 性自尔 (*"such is the nature"*) means: while phenomena appear vividly, their nature is precisely substanceless and without self-nature. Just like an image in a mirror: the image is clearly visible (not extinct), yet there is absolutely no real person in the mirror (not eternal / no self-nature). The annihilationist view leads people toward passivity and world-weariness, whereas "emptiness of the inner and outer" lets one, in facing all things, both perceive them clearly and remain completely unbound and unattached.
Misreading Two: Equating the "Inner Space Element" with "Physical Organs" and Reducing "Inner Emptiness" to "Cavities Inside the Body"
- Clarification: in the initial stages of meditation in the *Middle-Length Āgama*, the scriptures do indeed, for the convenience of beginners seeking liberation from the small-self attachment, borrow the physiological 「内空界」 (inner space element) — such as the oral cavity, throat, digestive tract, and other bodily cavities — for the deconstruction of attachment to space and matter [4241]. But one must never narrow "inner emptiness" down to "physiological cavities inside the body." In the complete doctrinal meaning, 「内法」 (inner dharmas) encompasses all six perceptual and mental mechanisms: eye, ear, nose, tongue, body, and mind [13033, 15764]. If one only treats the holes inside the body as inner emptiness, one completely misses the empty-deconstruction of "consciousness (mind base)" and "perception itself," and cannot break through the deepest psychological self-attachment.
Misreading Three: Believing That Perfecting "Emptiness of the Inner and Outer" Enables One to See a Mysterious State or Phenomenon Called "Emptiness" in the Mind
- Clarification: this is the 「取空相」 ("grasping the mark of emptiness") severely criticized in Mahāyāna scriptures such as the *Mahāprajñāpāramitā-sūtra*. The scriptures state that if a practitioner tries to make the mark of "emptiness of the inner and outer" appear or to obtain something (「使无相法出」, *"making the markless dharma emerge"*), this itself is a distortion of emptiness [13133]. "Emptiness" itself is also empty and still (内空内空性空, *"inner emptiness: the emptiness-nature of inner emptiness is empty"*) [13133]. True entry into the emptiness of the inner and outer is not imagining a void in the mind or forcing a particular "empty light / empty state," but thoroughly letting go of all reification of "the one who contemplates" and "the contemplated," of "inner" and "outer," and reaching the state of no attainment in which one is 「不不见色若相应若不相应」 (*"not not-seeing form, whether corresponding or not"*) and the mind abides nowhere [11584, 13133].