“Everything changes” is a familiar slogan. In the scholastic traditions of India, however, such a claim was never allowed to remain a slogan. For Dharmakīrti and the later Bauddha (Buddhist) logicians, the doctrine of kṣaṇikavāda—momentariness—was not a vague spiritual attitude but a sharp ontological thesis: whatever really exists (paramārthasat) is only a momentary particular (svalakṣaṇa), appearing in a flash and perishing as soon as it exerts its causal efficacy.

This view did not go unchallenged. Nyāya philosophers, committed realists, argued instead for enduring substances, stable properties, and a special relation of inherence (samavāya) binding them together. “Pots,” “flames,” and “selves” were for Nyāya continuants that persisted through change. The Bauddhas, by contrast, treated such continuants as conceptual constructions riding on streams (santāna) of momentary events.

To see what is at stake, it helps to follow one of Dharmakīrti’s central inferential strategies: from arthakriyā—causal efficacy or the capacity to perform a function—to the momentariness of whatever is causally efficacious. When carefully reconstructed, the argument shows why, on the Bauddha view, there can be no enduring pot, no substantial flame, and no lasting self—only sequences of discrete, causally potent flashes.

Arthakriyā: Existence as Causal Efficacy

For Dharmakīrti, to exist is to be capable of doing something. “Something” here is not vague; it is the concrete capacity to produce a specific effect. This is arthakriyā: the performance of a function, such as burning, illuminating, cutting, or supporting.

On this view, the criterion of existence is not being thinkable, nameable, or grammatically available as a subject of predication. It is acting. If x truly exists, then x must be able to participate in causal relations—to produce or block an effect, to contribute to some outcome. A purely inert “entity,” incapable of any causal role, is treated as indistinguishable from non-existence.

This functional criterion is not just a metaphysical preference. It is rooted in the Bauddha concern with pramāṇa theory—how valid cognition works. For Dharmakīrti, a cognition is valid if it leads to successful action. That success tracks the real causal powers of its objects; hence, what ultimately exists must be what underwrites that success. The measure of reality is arthakriyā.

Nyāya, interestingly, agrees that causal efficacy is an important marker of reality but refuses to equate existence with momentary efficacy. For Nyāya, substances endure and continue to ground causal powers over time. Dharmakīrti’s move is more radical: the causal power is not something a substance “has”; it is what the thing is, in that moment of acting.

From Causal Efficacy to Momentariness: The Basic Inference

One of Dharmakīrti’s core inferences can be rendered informally as follows. Consider a flame that burns a wick. Faced with this familiar scene, the Bauddha logician reasons:

1. Whatever possesses arthakriyā (causal efficacy) is momentary.
2. This flame has arthakriyā (it burns the wick, emits light, etc.).
∴ Therefore, this flame is momentary.

Nyāya would immediately question the first premise. Why assume that causal efficacy and momentariness are inseparable? To answer this, Dharmakīrti unpacks what it would mean for something enduring and numerically identical to exert causal efficacy across distinct moments.

Suppose, as Nyāya says, a flame is one continuous substance persisting while its color and shape change. Now ask: where, exactly, is the causal power located? If the enduring flame is wholly present at several times, then either:

(a) the very same entity, in virtue of the very same state, produces different effects at different times; or
(b) it produces the effect only at some particular time and not at others.

If (a), then the difference of times makes no explanatory difference; the same cause in the same condition would have to produce the same effect always, collapsing any distinction between “now” and “later.” If (b), then it is the state of the flame at the particular time—itself a temporally located event—doing the causal work. That state, in the Bauddha’s analysis, is already something momentary.

Dharmakīrti’s strategy is to push this point: effective causation is always tied to a concrete, temporally located, fully determinate presence. If there is any slack—if one and the same enduring thing can be equally present at different times without difference in its being—then the difference between those times cannot account for why an effect is produced now rather than earlier or later. The temporal difference becomes causally idle.

To avoid this, Bauddha Nyāya insists that an entity’s causal power is exhausted in a single, instant-like occurrence. Once that occurrence has done its work, it cannot do it again, under penalty of multiplying effects without new causes. Hence the first premise above: whatever has arthakriyā must be kṣaṇika, momentary.

Nyāya’s Realist Pushback: Substances and Inherence

Nyāya is not impressed. Its philosophers argue that our experience and our practices presuppose stable continuants. The pot that was on the floor in the morning is the pot we later see on the shelf. We remember it, refer to it, repair it. This thick sense of identity over time, they claim, is not illusion but a feature of how substances exist.

Nyāya ontology distinguishes substances (dravya) from qualities (guṇa) and motions (karman). A clay pot is a substance; its brownness, roundness, and coolness are qualities inhering in it; its being moved from floor to shelf is a motion. The glue that binds these layers is samavāya, inherence: a unique, intimate relation in which qualities and motions exist in substances, and parts exist in wholes.

On this model, causal powers belong primarily to substances but are exercised through their changing qualities and motions. The pot endures; its positional property and relations alter. In fire, Nyāya allows rapid change but still insists there is an enduring substance—fire—underneath the “flashing” appearances.

From this standpoint, the Bauddha reduction of all reality to momentary svalakṣaṇas looks like a confusion between how things appear and what supports those appearances. Yes, Nyāya concedes, there is a succession of states. But that does not mean there is no single thing that has those states. Continuity is not a conceptual fiction; it is what substances provide.

Svalakṣaṇa vs. Sāmānya-lakṣaṇa: Particular Flashes and General Features

The dispute over momentariness is also a dispute over what perception (pratyakṣa) reveals. For Dharmakīrti, the content of direct perception is always a svalakṣaṇa—a unique, utterly particular flash of reality. It is precisely this that has arthakriyā. The “this-ness” of a single instant of heat, color, or pressure is what actually burns, shines, or presses.

In contrast, the general features we think and talk about—“flame,” “pot,” “being brown”—are sāmānya-lakṣaṇas, general characteristics that arise through conceptual construction. They are not present in perception as such; they are imposed by thought, language, and habit.

When we see a fire, what is given in perception is, for Dharmakīrti, a sequence of distinct, non-repeatable svalakṣaṇas of color, heat, and so on. Only later does the mind overlay the concept “flame” and bind them into a single seeming object. That overlay is guided not by some metaphysical substance but by practical regularities in how these svalakṣaṇas have behaved: they have similar arthakriyā, so we treat them as “the same thing.”

Nyāya counters that universals (sāmānya) such as “pot-hood” or “fire-hood” are real, inhering in substances and making predication possible. When we say “this is a pot,” we are, according to Nyāya, recognizing an actually existent universal shared with other pots. The Bauddha reply is that such commonality can be explained in terms of exclusion (apoha): “pot” means “not non-pot,” drawing a boundary by leaving out everything that lacks the relevant functional profile.

Here the theory of meaning and the ontology of momentariness intersect. For Bauddha Nyāya, what is real in the strict sense are the instant-like svalakṣaṇas with their particular arthakriyā. Names and concepts latch onto streams of such events by excluding what does not fit the pattern. The apparent stability of “the flame” or “the pot” is a projection of this conceptual grouping, not a reflection of an enduring substance.

Continuity Without Substances: Santāna

A natural worry arises at this point: if everything is a momentary flash, how can there be any continuity at all—of objects, of memory, of moral responsibility, of practice? Bauddha Nyāya answers with the idea of santāna, a continuum or stream.

A santāna is not a separate thing over and above its moments. It is an ordered series of causally connected svalakṣaṇas. The “mental continuum” is a sequence of momentary mental events, each conditioning the next. The “flame” is a stream of heat-and-light-events, each generating conditions for a successor of similar profile. The pot, in the same manner, is a series of briefly existing configurations of particles with pot-supporting capacities.

Continuity, then, is explained through tight causal linkage rather than numerical identity. There is no single persisting self traversing experiences; there is a stream of experiences, each giving rise to the next in patterned ways. There is no enduring substance of the flame; there is a cascade of flame-moments, each with its own arthakriyā, related by causal dependence and resemblance.

Nyāya regards this as not enough. Without a single substance, it argues, we cannot account for genuine identity across change or for the subject who bears memory and agency. From the Bauddha side, however, these demands are precisely what needs to be relaxed. To require a metaphysically robust, unchanging subject is, they say, to extrapolate beyond what is given and to create the very target that Buddhist practice aims to dismantle.

Pramāṇa and No-Self: Logic in the Service of Soteriology

None of this is mere scholastic hair-splitting. Dharmakīrti is explicit that his logical and epistemological work serves soteriological ends. If valid cognition tracks arthakriyā, and if arthakriyā resides only in momentary svalakṣaṇas, then clinging to enduring substances and selves is, in a strict technical sense, a cognitive error: it constructs what is not there.

The no-self claim (anātman) is thus not simply a meditation theme; it is the upshot of a particular picture of what perception reveals and what causation requires. When I take myself to be an enduring subject, Nyāya’s kind of ātman, I am, on the Bauddha view, mistaking a santāna—a stream of mental svalakṣaṇas—for a unitary bearer. Logical analysis exposes that mistake by showing how continuity can be handled without positing a substantial self.

Conversely, meditation can be seen as training perception to align more closely with this momentary ontology. Attending carefully to transient sensations, thoughts, and moods, one begins to notice that what one habitually calls “my body” or “my mind” is already a moving tapestry of flashes. The doctrinal claim of kṣaṇikavāda is not imported into experience from above; it is articulated from the inside of such attention, then defended through rigorous argument against realist objections.

Practicing in a World of Flashes

How might this “world of flashes” orient practice without collapsing into generic mindfulness advice? One way is to treat the Bauddha analysis as a discipline of attention to arthakriyā. Rather than asking “What is this thing in itself?” one asks, moment by moment: “What is this event doing? What effect is it capable of now?”

Anger, for example, is not “my stable trait” but a particular svalakṣaṇa—a surge with specific arthakriyā: tightening the jaw, narrowing attention, prompting harsh speech. In the next moment, something slightly different is present, with a subtly different profile of efficacy. To see this fine-grained sequence is to weaken the intuition that there is a single angry subject who must defend itself across time.

Similarly, pleasure is not “my lasting happiness” but a brief, causally potent glow that inclines attention and action in certain directions. If its arthakriyā is clearly seen, its grip softens. The lure is not to deny the glow but to avoid upgrading it into a permanent possession.

In this way, the Bauddha picture encourages a practice of discriminating perception: noticing how each instant of experience both arises from conditions and immediately becomes a condition for the next. The self is no longer a central owner but a name for a santāna in which causes and effects flash by. Clinging requires the fiction of a stable something to cling to and with. Momentariness undercuts both sides at once.

Yet the point is not to despise continuity or to deny the pragmatic usefulness of “persons,” “pots,” and “flames.” Concepts, on Dharmakīrti’s view, remain indispensable at the level of everyday dealings (saṃvṛti). The task is to hold them lightly, knowing that they ride on vast networks of svalakṣaṇas, and that none of these, individually or collectively, can be frozen into an independent substance or self.

In the end, the debate between Bauddha momentariness and Nyāya substance-realism is not only about metaphysical taste. It concerns what we are licensed to posit, given what perception and inference can justify, and how those posits shape the forms our attachment takes. Whether we side with Dharmakīrti or with Nyāya, the controversy invites a closer look at the very things we usually find most obvious: that a pot is just there, that a flame simply burns, that “I” am the one to whom all this happens.

If we took seriously the idea that whatever truly exists does so only in the mode of a vanishing flash, how might that alter the way we look at a single breath, a single word spoken, or a single impulse to grasp?