Shcherbatskoy wrote in "Buddhist Logic" (translating Dharmakirti's Logic Manual) something like this:
Senses can directly perceive only one 'moment', but there is a 'chain of moments' that enters our consciousness, thanks to the activity of mentation (which unites them in regard to that moment) on the basis of sensual perception.
Only a chain of moments can enter the consciousness on the basis of perception, because one moment cannot be apprehended by consciousness.
As I understand, it means we build our knowledge not on the basis of those momentary discrete appearances, but on the basis of something like their superpositions, somehow prolonged in time.
But that leads me to another question: are these momentary and discrete things actually real?
It seems possible that "momentary" and "discrete" are just our ideas.
Maybe there's nothing really "momentary and discrete" at all.
PS to explain more:
(1) More on Svalakshana, read Shcherbatskoy: The Buddhist Logic. It's a well known book, where he translates and comments Dharmakirti. I have only Russian edition, so I myself translated the quotation above to English, which might introduce some inaccuracies, as I'm not a native speaker.
Also I found an interesting article by Victoria Lysenko, who explored exactly those problems - sense perception (pratyaksha), conceptualizations, etc. In an article "Svalakshana" in Russian Encyclopedia "Philosophy of Buddhism" she says that Svalakshana is somehow a controversial term, understood differently in Sautrantika and Yogachara.
I don't know is there this text anywhere in English, so here is the Google-translation with several my corrections:
[The opposition] Svalakshana - samanya-lakshana (Sanskrit svalakshana: literally "characterizing / defining itself". Sämänya-lakshana: "defining through the common [with others]") - the terms of the epistemology of the Dignaga and Dharmakirti schools, denoting individual, concrete, singular, unique - "particularity", in contrast to the general characteristic - "universalia". Svalakshana is something that is perceived in itself, as a reality, independent of any other things, whereas samanya-lakshana is the result of comparison, comparison of the given perception with something else, or their perception in some capacity, in some role, in otherness. Between them there is an impassable abyss: the svalakshanas are changeable, or rather, instantaneous (see Kshanikavada), and the general characteristics, on the contrary, are stable. Since reality, from the POV of Buddhists, is a discrete flow of dynamical point events - dharmas, then svalakshanas are real, while Samanya-lakshanas are mentally constructed.
The opposition Svalakshana - Samanya-lakshana goes back to the abhidharmic opposition of the truly existing (dravyasat) and nominal (prajnaptisat) dharmas, where the former are endowed with their own nature (svabhava), and the latter are declared unreal. In abhidharma schools, svalakshana is the self-nature of the phenomenon, distinguishing it from other phenomena, or a specifying characteristic (eg, svalakshana of Earth - resistance, of Fire - burning, etc.). Ontologically, S. - S.-l. become these units of analysis in the philosophy of Dignaga-Dharmakirti.
Dharmakirti puts forward a number of criteria that distinguish svalakshana from samanya-lakshana: the ability to produce effects in the form of expedient actions (artha-kriya-shakti), dissimilarity [with nothing else] (asadrishta), nonspecificity by word, perceptibility regardless of any other factors (such as agreements on the use of words, etc.) (Pramana-Varttika III, 1-2).
According to Dharmakirti, actual existing svalakshanas are perceived in two ways: in their own form (svarupa) and in the form of something else (pararupa), i.e. in the form of generalization. Hence two tools of reliable knowledge (pramana): direct perception (nirvikalpaka-pratyaksha) - for svalakshanas, and logical cognition (anumana) - for samanya-lakshanas.
If there is almost no disagreement in the interpretation of Samanya-lakshana, since this term is unambiguously associated with mental construction (kalpana, vikalpa), which is in Buddhist Epistemological School of Dignaga-Dharmakirti belongs to the category of non-genuine, conditionally-true being (parikalpita; see Trisva-bhava), then there are different, often mutually exclusive opinions about the much more complex and ambiguous concept of svalakshana, sometimes even from the same author. For example, Shcherbatskoy, on the one hand, saw in this term an analogue of the Kantian noumena and "things in themselves"; on the other hand, he likened the svalakshanas to "sensory data", sense data, sensibilia (Stcherbatsky 1930, vol. 1, p. 68, 79, 87 ). The difficulty of interpreting Svalakshana is that in the teachings of Dignaga and Dharmakirti, the position of the epistemological idealism of Yogachara is combined with realistic position of Sautrantika. Amar Singh, criticizing Shcherbatskoy's attempt to bring the concept of Svalakshanas closer to Yogachara idealism, notes that the real opposition of the Svalakshana as the ultimately particular object of perception to Samanya-laksana as an object of logical cognition is possible only within the realistic theory of knowledge of Sautrantika (Singh 1984). From the point of view of Sautrantikas, cognition does not deal with external objects, but only with their representations in consciousness - sensory data, which, however, are caused by objectively existing external stimuli. It is these stimuli that are called in Sautrantika Svalakshanas. From the position of Yogacharas, once cognition is independent of external objects, svalakshanas can only be sensory data. In the works of Dharmakirti, the term svalakshana is used, as a rule, in the context of the realism of Sautrantika. However, here arises the problem of the relationship between the Svalakshanas and their sensory reflections in cognition, images (abhasa, akara): are these images similar or different to their svalakshans?! Are svalakshanas noumenas or are they knowable?
Dharmakirti did not give direct, unambiguous and consistent answers to these questions. First, he adhered to the Sautrantikan concept of similarity (sarupya) between the cognitive image and his real prototype, i.e. external object (see Sakaravada - Nirakaravada), and secondly, he acknowledged that the svalakshanas are "grasped" (grahya) by pratyaksha (sensory perception, sensation), which implies that they can not be noumenal. But then in what sense can we speak about their inaccessibility to verbal expression? In Buddhist epistemology this is explained, first, due to the instantaneousness of the Svalakshanas (see Kshanikavada), because of which they can not be objects of empirical experience, which is a mixture of instantaneous sensations with their conceptualization - kalpana (only buddhas and other enlightened beings are able to recognize kshanas), and secondly, by Buddhist nominalism - the conviction that the meaning of words is only mentally designed universalia. Therefore, the verbal ineffability of Svalakshanas does not imply their transcendence in relation to perception. Against the noumenality of the Svalakshanas is also the fact that Dharmakirti speaks of Svalakshanas as atoms (paramanu - meaning Buddhist "phenomenal" atoms of colors, tastes, etc. qualities). Though, he does not develop this idea; so researchers argue about whether he understands by Svalakshanas individual atoms or their clusters (samchita) and, accordingly, whether the atoms generate one sensation (sensum, eg, a color spot) or a set of atomic sensations, which are then synthesized into color spots.
Analysis of new sources, inaccessible in the times of Scherbatskoy, especially Skt. and Tib. commentaries of the followers of Dharmakirti, allow to better understand the dilemma faced by the Buddhist philosopher. If he recognizes that the svalakshanas are single atoms, then this will contradict the Buddhist postulate of the non-perceivability of individual atoms (from the POV of Buddhists, atoms are perceived only in mass, like hair); but if he would assert that these are aggregations of atoms, he will face the objection that the accumulation of atoms, as representing "single in many", is actually a universal (samanya-lakshana), and, cognizing it, sensory perception turns to be conceptual (Pramana Varttika III. 194). In response to this objection, Dharmakirti denies the possibility for one object to be both single and multiple at the same time, citing the example of a multicolor on the wings of a butterfly, which is perceived as a single color (the reference to the well-known concept of the "motley" color "chitra" in the Vaiśeṣika and Nyāya schools, which is not a collection of different colors, but an independent color). According to the commentators, Dharmakirti interpreted the cluster (samchita) of atoms not as a whole (avaya-vin), different from the sum of its parts (avaya), but as an impulse acquired by each individual atom as a result of the impulses of other individual atoms entering the causal complex (hetu-samagri), which generates the sensible given. Since in Dharmakirti's teachings it is the Svalakshanas that are causally effective (artha-kriya-karitva) stimuli of perception, and therefore the only real entities, they should be identified not as a collective impulse of all atoms, but rather as a complex of interdependent impulses of individual atoms (Dunne 2004, p.103-109). This interpretation ultimately proves to be close to one of Shcherbatskoy's interpretations, who often compared svalakshana to energy point-moment. ("External object is not matter, but energy ... reality is instantaneous and consists of moment-points, which are centers of energy" - Shcherbatsky 1930, vol. I, p. 510).
However, the question remains open: what is the content of this sensory given - a mere reflection of the Svalakshanas, which by definition are non-spatial, - or it is an image, for example, of a color (a color spot) having a spatial extent? Dharmakirti does not give an answer, but it is obvious that the lack of spatiality of the Svalakshanas jeopardizes the principle of congruity (sarupya) of the cognitive image and its external referent, to which he was committed. Critical analysis of the concept of S. - s.-l. of Dignaga and Dharmakirti was performed by the Madhyamik-Prasangik Chandrakirti.
REFERENCES: Stcherbatsky Th. The Buddhist Logic. Vol. 1-2. Leningrad, 1930-1932; Singh A. The Heart of Buddhist Philosophy - Dinnâga and Dharmakïrti. D., 1984. P. 117-137; Dunne JD Foundations of Dharmakïrti's Philosophy. Bost., 2004. P. 91-113; Arnold D. Buddhists, Brahmins, and Belief: Epistemology in South Asian Philosophy of Religion. NY, 2005.
V.G. Lysenko. Source - Encyclopedia Philosophy of Buddhism - Russian Academy of Sciences, Institute of Philosophy
That's an interesting text, and there are more interesting articles by Lysenko - on Dignaga, Dharmakirti, Vasubandhu, Vachaspati Mishra etc., e.g. "What is immediate perception? The Buddhist answer". Download PDF here: http://www.iias.asia/sites/default/files/IIAS_NL44_2021.pdf
or from Academia.edu: https://www.academia.edu/8135589/What_is_immediate_perception_The_Buddhist_answer
(2) So if you asked what I think, I approach it from Madhyamaka (as I understand it). Or, in modern logic, from what they call "constructivism". How did ideas of "momentary" and "discrete" appear in our thinking?
They might look self-evident, from the point of view of our experience:
- a book moved by my hand seems to be a discrete object;
- and an idea of "zero-length moment" comes from imagining a frozen cut of the world...
But does "zero-length moment" have any reality except being our imagined concept?
Then are we sure that separate moments exist at all - even of non-zero length?
What if the world and the time are not discrete at all, in any sense?
Then how can we speak of elementary constituents of our perception as discrete momentary things?
Did you ever perceive really discrete momentary perceptions? Even a flash of lightning is not a discrete perception, because it has a "tail" of subsiding blindness.
So isn't "discreteness of moments" just a mental construction which we use to cut the world in our imagination?
I.e., "discreteness" might belong only to our mental constructing, but not to primary sensory data or their sources.
Do these questions make sense?
Then, speaking about discrete things, are they really discrete, or that discreteness exists only in our modeling of the world?
Is the book in my hand really discrete thing, or that is just an illusion, developed in my mind?