Version 0.1, Written for my mother who requested for an explanation of Heart Sutra.

The Unfindable Fullness: How a Drum, a Rainbow, and a Mirage Unlock the Heart Sūtra

The Heart Sūtra presents a profound challenge to our everyday perception. Its central declaration, “form is emptiness; emptiness is form,” and its sweeping negations—“no eye, no ear… no mind… no attainment”—can easily be mistaken for a nihilistic denial of the world. Yet, this radical teaching is not about annihilation but about de-reification: a precise dismantling of our tendency to project solid, independent existence onto a fluid, interdependent world. To truly grasp this, we need not leap into abstract philosophy but can begin with tangible, elegant analogies found within the Buddhist tradition itself. The sound of a drum, the appearance of a rainbow, and the eight classic examples of illusion reveal that emptiness, or śūnyatā, is not a void but the very unfindability and lack of an independent core that allows phenomena to manifest vividly and function flawlessly.

The Drum: Emptiness as the Unfindability of Essence

The analogy of the drum, detailed in The Questions of an Old Lady sūtra (Mahallikā­paripṛcchā, Toh 171), provides the foundational logic. When a drum is struck, a sound arises. Our immediate instinct is to locate this "sound." Is it in the wood frame? The stretched hide? The stick? The hand that strikes it? The sūtra systematically deconstructs this search, concluding that “The sound does not dwell in the wood… hide… stick… [or] the person’s hand.” The sound is utterly unfindable in any of its constituent parts, nor does it exist as a separate, free-floating entity apart from them. This investigation is a search for the sound's essence or core—a self-sufficient "sound-thing" that can be pinned down. The failure to find such a core reveals its emptiness.

Because no self-contained "sound-thing" can be located, what we conventionally call its "existence" is revealed to be nothing more than a dependent designation—a label we apply to this functional confluence of conditions. This points to the crucial Middle Way, which is free from the extremes of existence and non-existence. The sound is not an inherently existing entity (eternalism), nor is it a complete nothingness (nihilism), since it clearly functions. Its functioning is purely conventional, designated upon dependencies. Remove any one condition—the hide, the effort, the air to carry the vibration—and the sound vanishes. The sūtra is explicit: “Because of these conditions, it is termed sound… That which is termed sound is also empty. It has no coming. It has no going… all phenomena are inherently stopped.” (Mahallikā­paripṛcchā, Toh 171, 84000). It doesn't travel from a sound-realm to our ear. This is the essence of what the Heart Sūtra compresses into the terms “unborn, unceasing.” The drum’s sound is empty of a findable, static core, and precisely because of this unfindability, it can arise and function unmistakably when conditions gather.

(Parallel note: the same sūtra generalizes the point to birth/death and to the aggregates and sense-consciousnesses—stating they have “no producer,” do not come or go from anywhere, and are designated on conditions. This anticipates the Heart Sūtra’s triad negations.)

The Rainbow: Vivid Display and Luminous Knowing

The rainbow offers a brilliant visual parallel, illustrating the principle of vivid display that is nowhere stored. A rainbow appears as a dazzlingly precise and vibrant arc of colour, yet it has no substance or location. It requires a specific convergence of conditions: sunlight, water droplets suspended in the air, and an observer positioned at the correct angle (~42°); move slightly and ‘the rainbow’ is gone—there was never a ‘thing’ hiding anywhere to begin with. It never came from anywhere, isn't hidden in the droplets or the sun, and doesn't retreat to a secret place when it disappears. (On the ~42° geometry of primary rainbows, see NOAA SciJinks.)

This introduces a crucial complement to emptiness: luminosity (Pāli pabhassara, Skt. prabhāsvara). This quality does not refer to literal light, like that from a lamp, but to the pristine knowing quality of consciousness—the vivid, clear presence that is the very knowing of any experience (cf. AN 1.49–52: “Luminous, monks, is the mind…”). There is no knowingness apart from the vivid appearances themselves; the knowing is the appearing. Crucially, this pristine consciousness is not a separate, underlying substance or a "True Self." Just like the rainbow, this luminous knowing is itself empty of intrinsic existence. It is not a subjective cognition illuminating an objective appearance; rather, phenomena are realized to be the nondual, self-luminous display—and this very luminosity, too, is empty of own-nature. This is the inseparability of clarity and emptiness, recognizing that a separate subject and object never arose in the first place. The world of form is not a dull, empty void; it is a radiant, clear, and vivid display of our pristine consciousness, and our experiencing of it is this very luminosity.

The Eight Illusions: The Union of Appearance and Emptiness

To deepen this understanding, the Mahāyāna tradition employs the eight examples of illusion. (Traditional enumerations of these eight similes vary slightly across texts and lineages; see also the Foam Sutta, SN 22.95, for closely related imagery of insubstantiality.) These similes are not meant to suggest the world is "fake" but to train the mind to see that all phenomena are illusory. The distinction is crucial. To call something "fake" implies a binary opposition to something "real"—a counterfeit bill versus a genuine one, a hallucination versus a verifiable object. This view still operates within a framework that assumes a baseline of inherent, solid reality. To say phenomena are illusory, however, is far more subtle. An illusion, like a mirage, is not nothing; it appears vividly and functions conventionally (it can cause thirst and hope). But when its nature is investigated, it is found to be completely dependent on causes and conditions, empty of any findable, independent essence of its own. Thus, "illusory" affirms the conventional appearance while revealing its ultimate, empty, and non-arisen nature.

Each example reveals how the luminous appearance of phenomena—their inseparable clarity and display—is inseparable from its unfindable, insubstantial nature. Furthermore, they point to the “emptiness of emptiness”—the profound realization that there is no hidden truth or void behind these appearances. Penetrating their emptiness leads one back to the surface of the everyday, revealing that all things have "one nature, that is, no nature."

A Mirage: In the desert, the vivid presence of shimmering water arises with powerful, functional clarity, dependently originating from conditions of superheated air, light, and a perceiving mind. This potent display is inseparable from its complete insubstantiality. When examined carefully, as the Buddha taught in the Pheṇapiṇḍūpamasutta (SN 22.95), the mirage appears completely vacuous, hollow, and insubstantial. For what core could there be in a mirage? The knowing of 'water' and the emptiness of water are not two; the vividness is the groundlessness. This reveals the emptiness of emptiness: there is no deeper truth of 'nothingness' hiding behind the mirage. The shimmering, deceptive surface is the entire groundless display of the event. Penetrating its emptiness simply returns us to the vivid, ungraspable appearance itself.

The Moon's Reflection in Water: The reflection is a perfect, radiant knowingness—clear, bright, and detailed. Its appearance is entirely dependent on a confluence of conditions: the celestial body we designate as "the moon," the reflective surface of the water, and the specific angle of the observer. While one might first realize this radiant knowingness and reify it—first as a timeless, eternal witness or 'I AM'—deeper insight is needed. Even after the illusion of a separate knower is seen through, this radiant knowingness as a vivid display can still be mistaken for a truly existing, external world. It is only the subsequent, penetrating insight into the dependent origination and empty nature of all phenomena that reveals this very radiance to be, by its nature, completely illusory and empty of any findable core. The clarity of the reflection and its emptiness are inseparable. This logic applies all the way up: the "real moon" is also a dependently originated phenomenon. Thus, the reflection is an illusion of an illusion. Its ultimate nature is therefore 'no nature.' Realizing its emptiness doesn't reveal a void; it reveals the vivid, shimmering reflection as the complete, groundless presencing of that moment.

A Dream: The dream world is a totally immersive field of vivid presence—sights, sounds, and intense emotions feel completely real, arising in dependence on the sleeping mind and karmic traces. This immersive vividness is inseparable from its complete lack of a locatable essence. When examined upon waking, the entire dream world is found to be hollow and insubstantial, for what core could there be in a dream? The presencing of the dream is its fundamental groundlessness. There is no ontological depth lurking beneath the dream's deceptive surface; the vivid, transient dream-world is the whole story, seen without the illusion of a solid ground beneath it.

A Magical Illusion: A magician's display conjures the potent display of a horse, so convincing it captivates the audience. This convincing presence dependently arises from the magician's skill, props, and the audience's perception, and is, by its very nature, unfindable. When examined carefully, the display is revealed to be vacuous and hollow, without any real substance. For what core could there be in a magic trick? The inseparable union of this vividness and its emptiness is what makes it illusory. Penetrating the illusion doesn't lead to a hidden truth, but back to the conventional world of the magician, the props, and the audience—the luminous and conventional surface of things.

An Echo: An echo manifests as a clear, distinct presence of sound, arising in dependence on an initial sound, a reflective surface, and a medium like air. This audible clarity is inseparable from its complete lack of an independent source. When examined closely, it is found to be hollow and insubstantial, for what core could there be in an echo? The knowing of the sound is its essenceless nature. The clear sound and its emptiness are not two. Realizing this, one finds that the echo's ultimate nature is simply its own audible, transient, and groundless appearing.

A City of Gandharvas: This atmospheric illusion appears as a grand, complex, and radiant knowingness, dependently arisen from clouds, light, and atmospheric conditions. This magnificent appearance is inseparable from its utter insubstantiality. When examined, it is seen to be completely vacuous and insubstantial, for what core could there be in a city in the clouds? Its vividness is its groundlessness. There is nothing beneath this deceptive surface; its vivid, illusory appearance is the whole of the event.

A Phantom: An apparition can appear with terrifying, vivid presence, its appearance dependent on certain mental or causal conditions. This powerful appearance is inseparable from its complete lack of any findable core. When examined, it is revealed to be hollow and insubstantial, for what core could there be in a phantom? The terror it may induce is not inherent to the phantom but arises from failing to recognize its empty, illusory nature. When its emptiness is seen, the vivid presence remains, but the fear, which depends on reification, dissolves. The knowing of the apparition and its groundlessness are a single, inseparable event.

A Reflection in a Mirror: The image in a mirror is a perfectly clear, precise, and radiant knowingness, dependently originated from your face, the mirror's surface, and light. When we investigate this vivid presence, we find that no inherent essence can be located, either in the appearance itself or in its clarity. When examined, the reflection is found to be completely vacuous and hollow, for what core could there be in a reflection? This inseparable union of a vivid, knowing appearance and an unfindable essence is what makes it illusory. To be ultimately empty is, ultimately, to lack emptiness. The reflection's nature is simply its own clear, dependent, and vivid appearing on the surface of the mirror.

Each of these examples hammers home the central point: all phenomena are illusory. Their luminous presence is not separate from their unfindable nature—the inseparable union of clarity and emptiness. Form is emptiness, emptiness is form. They are not two separate qualities but a single, indivisible display. They dependently arise as a vivid, spontaneous presence; this appearance, when cognized conceptually, is a dependent designation, and this very appearing, this vivid knowingness, is its groundless, essenceless nature.

Deconstructing the Perceptual Triad: “No Eye… No Form… No Consciousness”

With this foundation, we can approach the Heart Sūtra's most challenging passage. The Heart Sūtra (Toh 21) compresses this into a few strokes: “Form is emptiness; emptiness is form… in emptiness there is no eye, no ear… no mind; no ignorance and no end of ignorance… no attainment.” (84000). This sweeping negation is a concise and systematic deconstruction of the entire perceptual process, resolving the false dichotomy between mind and matter. (For a practice-driven unpacking, see the ATR posts "Mind, Matter, and the Middle Way" and "A Practitioner's Reflection on the Kōmyōzō Zanmai".)

The Sūtra's shorthand dismantles the entire perceptual triad by negating the inherent existence of each of its components:

“No Sense Faculty” (no eye). What makes a lump of tissue an eye? Only its relational function in a seeing-event. Take away either a visible form or the corresponding consciousness and it’s not functioning as an eye. So “eye” is dependently originated, and because it is so, it’s empty of any findable essence and is merely a dependent designation—a valid label based on conditions and functions, nothing intrinsic. (See SN 35.93 on contact as the meeting of the three.)

“No Sense Object” (no form). What is a "form"? As a visible form, it’s defined relationally—as what stands in the right relation to a visual faculty and a visual consciousness. Its object-of-sight-ness is not an intrinsic property, but designated dependently within the triad. Thus, as a perceived form, it’s empty and merely designated in dependence on the other two.

“No Sense Consciousness” (no eye-consciousness). Consciousness is always consciousness-of; it never arises “in a vacuum.” The Buddha states repeatedly that consciousness arises in dependence and “apart from a requisite condition there is no origination of consciousness” (MN 38). Hence it too lacks any independent core and is empty and dependently designated (we call it “eye-consciousness” precisely when eye and form converge).

Putting it together. The triad—faculty, object, consciousness—is a single, momentary, dependently arisen event (contact is “the meeting/convergence of these three,” SN 35.93). Because none of the three can be established on its own, the Heart Sūtra can say “no eye … no form … no eye-consciousness” in emptiness—it’s denying intrinsic nature, not everyday function. (A related early image is the “two sheaves of reeds” leaning against each other to illustrate mutual dependence—SN 12.67.) And Nāgārjuna clinches the logic:

“Whatever is dependently arisen—that we declare to be emptiness; that, being a dependent designation, is itself the Middle Way.” (MMK 24.18)

(Terminology note: the Sanskrit term here is upādāya-prajñapti, “dependent designation.” The point is that dependence is not a real mode of being that things “borrow”; rather, because things are dependent, they are empty—and so our talk about them is valid convention, without reification.)

The Practical Path to Insight: From Luminous Mind to Emptiness

While the Heart Sūtra presents the ultimate view of emptiness, the experiential path to that view is crucial. In this commentary, I delineate a path that unfolds in phases, based on my interpretation of texts from the Zen tradition like the Kōmyōzō Zanmai (Treasury of Light).

Phase 1: The Foundational Realization of Luminous Presence ("I AM"). The essential first step is to realize the "luminous Mind" itself—the ever-present pure Presence and capacity of Knowingness that is the baseline fact of all experience. This provides the stable ground from which to explore the profound truth of non-duality and emptiness, even though Presence is still falsely reified as an eternal Witness at this stage.

An Intermediate Phase: Substantialist Nonduality ("One Mind"). Following the "I AM" realization, a practitioner often enters a profound non-dual state where all phenomena are seen as the display of a single, unified Mind. This is a powerful insight, but it can become a subtle trap as one continues to reify "Mind" as a truly existing, ultimate substance that is nondual with everything, or modulates as everything. This is a substantialist view and must be penetrated by the deeper wisdom of anātman, which reveals that this luminous knowing is itself dependently arisen and empty.

Phase 2: The Deepening Insight into Anātman and Emptiness. Once this luminous ground is realized, the path then turns the light of inquiry back upon itself.

• Emptiness of Self (pudgala-nairātmya): The practitioner investigates this luminous Mind and discovers it is empty of any inherent, independent self-nature (svabhāva).
• Emptiness of Phenomena (dharma-nairātmya): The insight then deepens to perceive the empty, dream-like nature of all appearances.

This progression is vital. By first realizing the luminous, vivid nature of Mind and appearance, the subsequent insight into their emptiness does not lead to nihilism. Instead, one realizes that phenomena are like a rainbow: vividly apparent, yet utterly empty.

Scaling the Principle: From Drums to Buddhas

This principle scales universally. The Ornament of the Light of Awareness (Toh 100) uses the example of a cloud, stating, “the cloud is non-arisen and non-ceasing; free from coming and going.” Strikingly, it then applies this very same logic to the Tathāgata, whose appearance is for the benefit of beings yet is ultimately as non-arisen and unceasing as the cloud. (84000 translation; see the rain-cloud analogy.) This logic culminates in Nāgārjuna's famous verse: “Whatever is dependently arisen, we declare that to be emptiness; It is a dependent designation; Just that is the middle path” (MMK 24:18).

Conclusion

In conclusion, the Heart Sūtra’s wisdom is unlocked when we see that emptiness is not an absence but a dynamic potential. Because the drum’s sound is unfindable in any single part or apart from its conditions, its very emptiness is what allows it to manifest unfailingly as a luminous, dependently-designated display. Everything in our experience—from the sound of a drum to the luminous appearing of a mirage—functions on this same principle. By first grounding ourselves in the direct realization of luminous presence, we can then safely and profoundly realize the truth to which the Sūtra points: that all phenomena, including the mind itself, are unborn and unceasing. This is not an erasure of the world, but the revelation of its true, magical nature: a vivid, functional, and radiant display, utterly free of any solid, findable core.

References (primary & supporting)

• The Questions of an Old Lady Sūtra (Mahallikā­paripṛcchā). Toh 171. 84000: Translating the Words of the Buddha. (Drum-sound passage: “Because of these conditions, it is termed sound… no coming, no going… all phenomena are inherently stopped.”)
• The Perfection of Wisdom, The Heart Sūtra. Toh 21. 84000: Translating the Words of the Buddha. (“Form is emptiness… in emptiness: no eye… no mind… no attainment.”)
• The Ornament of the Light of Awareness That Enters the Domain of the Tathāgatas. Toh 100. 84000: Translating the Words of the Buddha. (Cloud/Tathāgata non-arising, “free from coming and going.”)
• Nāgārjuna. Mūlamadhyamakakārikā (MMK) 24:18. (Dependent arising = emptiness = dependent designation [upādāya-prajñapti].)
• Saṃyutta Nikāya (SN) 35.93. Contact defined as the meeting/convergence of faculty, object, and consciousness.
• SN 12.67. “Two sheaves of reeds” simile for mutual dependence.
• Majjhima Nikāya (MN) 38. “Apart from a requisite condition, there is no origination of consciousness.” (Refutation of a transmigrating, selfsame consciousness.)
• Aṅguttara Nikāya (AN) 1.49–52. “Luminous is the mind” passages; luminosity as baseline capacity, not an uncaused essence.
• SN 22.95 (Pheṇapiṇḍūpamasutta / Foam Sutta). Aggregates likened to foam, bubble, mirage, plantain trunk, and a magic trick—insubstantiality imagery.

References (secondary & explanatory)

• “Mind, Matter, and the Middle Way.” Awakening to Reality.
• “A Practitioner’s Reflection on the Kōmyōzō Zanmai.” Awakening to Reality.
• NOAA SciJinks. “How Is a Rainbow Formed?” (Observer-angle ~42° of primary rainbow.)
• Rigpa Shedra Wiki. “Eight Similes of Illusion.” (Overview of enumerations.)

(Terminology: śūnyatā; Pāli pabhassara / Skt. prabhāsvara for “luminosity”; upādāya-prajñapti = dependent designation.)