Enlightenment: Sudden or Gradual?

Legend has it that the Buddha gave as many as 84,000^[1] lectures that Buddhists are expected to study. Buddhists also have a good number of moral rules to follow. On top of these, they are required to practice meditation. Enlightenment may be achieved through the study of scriptures, continuous moral conduct, and prolonged periods of deep meditation. If one must satisfy all these requirements for her enlightenment, it is reasonable to believe that enlightenment cannot be achieved effortlessly or instantaneously. Sudden enlightenment, the enlightenment to be achieved all at once, seems impossible. Many of us would assume that achieving enlightenment requires one to devote a great deal of time and effort. Even the Buddha spent six years to obtain it, didn’t he?

To our surprise, however, it is sudden enlightenment that has been accepted as the only true enlightenment among many Zen traditions in East Asia. According to these traditions, enlightenment should come naturally, effortlessly, and often passively, all of a sudden and all at once — otherwise, it is not genuine enlightenment. Apparently, this view of sudden enlightenment conflicts with the teachings of all the other Buddhist traditions that claim to conscientiously follow the teachings of the Buddha himself.

For instance, Buddhists are supposed to tread the Buddha’s Noble Eightfold Path — right view, right speech, right concentration, etc. — to eliminate suffering, achieve enlightenment, and obtain nirvana. Each of these eight paths has intermediary steps one should take. All these intellectual trainings, moral practices, and spiritual cultivation require conscientious efforts to be sustained for extensive periods of time. The Buddha’s teaching of eight right paths seems to make only gradual enlightenment possible. Almost all other schools outside Zen traditions require some significant study of scriptures, cultivation of moral virtues, and meditation practices as necessary conditions for achieving enlightenment. Sudden enlightenment seems to be out of the question. But then, how have Zen traditions almost uniformly maintained their claim of sudden enlightenment as the only genuine form of enlightenment for more than a millennium?

The time-honored debate on sudden and gradual enlightenment (頓漸論爭) originated, as I will argue below, from conceptual confusions and the misunderstanding of each other’s philosophical stances. For one thing, we do not seem to have a clear understanding of the concept of sudden (頓). For another, it is not always clearly stated whether this sudden/gradual debate is about enlightenment, about the process of moral/spiritual cultivation (修), or about the system of teachings (敎) of different Buddhist schools. There also is a misunderstanding that might have resulted from the controversial issue on the existence of Buddha-Nature (佛性). Many Zen traditions have accepted the view of innate Buddha-Nature as one of their most important philosophical foundations. As I wrote in the previous chapter, scholars have recently begun to criticize this idea of Buddha-Nature, though, by claiming that Buddha-Nature is in fact identical with ātman of Brahmanism. The Buddha clearly denied the existence of ātman with his teaching of non-self (anātman). Buddhists should not accept any view that is contradictory to the Buddha’s view of non-self. I believe that the sudden/gradual debate has often proceeded ignoring these differences and conceptual confusions. The clarification of these confusions and misunderstandings would provide us with a better grip on the problem itself and possibly help us settle the debate.

Since the birth of Zen in China, their traditions have focused on the issue of sudden/gradual enlightenment. As noted above, however, the sudden/gradual debate has been extended to the process of moral and spiritual cultivation. The main theme has been: Is prolonged cultivation necessary after enlightenment, especially after sudden enlightenment? Suppose someone has achieved her sudden enlightenment (頓悟). Does she still need to continue her moral and spiritual cultivation when she is already enlightened? Many Zen masters have believed that she has to. For old (bad) habits die hard, and they continuously produce negative effects that may undermine her enlightenment itself. She needs to continuously resist and try to eliminate those bad habits to remain solidly enlightened. This process of complete elimination of old habits takes time. This is why, these Buddhists claim, sudden enlightenment should be followed by gradual cultivation (頓悟漸修). Others have disagreed. For these masters, her sudden enlightenment is not enlightenment at all if she still requires further moral and spiritual cultivation. That is, sudden enlightenment should include sudden cultivation (頓悟頓修).

I will return to this issue of sudden enlightenment gradual cultivation (頓悟漸修) and sudden enlightenment sudden cultivation (頓悟頓修) after I clarify the concept of sudden along with the concept of enlightenment. Also, some Buddhist schools have claimed that their views are sudden teaching (頓敎) — the highest, ultimate teaching of the Buddha that leads one directly to ultimate enlightenment — and accordingly that they are superior to other schools that espouse gradual teaching (漸敎). Since the debate on sudden/gradual teaching requires a comprehensive survey of the views of different Buddhist schools, however, we must set it aside for other occasions. Here, we will discuss mostly the sudden/gradual debate on enlightenment.

The sudden/gradual debate is fundamentally about the process or the method through which enlightenment is to be achieved. The words “sudden” and “gradual” are primarily about temporal durations, so the sudden/gradual debate might be about the short or long time period we need to achieve enlightenment. As I will show below, however, “sudden” might also have to be understood as describing some logical nature of enlightenment. Since we may require a short or long time to achieve enlightenment depending on the features of enlightenment, the sudden/gradual debate needs to be understood in relation to the nature of enlightenment. It is thus necessary to analyze first the concept of enlightenment. We will then examine if enlightenment is to be achieved suddenly or gradually.

In “Chapter 4 Concepts of Enlightenment,” I classify three different kinds of enlightenment — philosophical enlightenment, nirvanic enlightenment, and enlightenment in Zen traditions. We will briefly revisit each of these three kinds of enlightenment and see how each enlightenment is obtained. We are going to see that enlightenment, if understood as an empirical process, is always gradual enlightenment; but I will also argue that philosophical enlightenment, if construed from a logical point of view as a paradigm change^[2] in one’s belief system, is sudden enlightenment.

1. Philosophical enlightenment and sudden enlightenment

Enlightenment is originally and fundamentally an epistemic achievement. It is basically about the realization of the truth of self and the world. The Buddha teaches that there is no self and that everything in the world arises^[3] depending on its conditions. Enlightenment requires our understanding of this philosophical truth of non-self and dependent arising. Since no one has a self, and since everything arises only dependently on its conditions, nothing can exist on its own and everything lacks self-existence and intrinsic nature.^[4] The Mahayana traditions of Central and East Asia embrace this philosophical truth of Buddhism with their claim of emptiness. If there is a self, it must constitute the essence of a given person. But since this person lacks her essence, there is no self. The truth of non-self is implied by the truth of emptiness. Also, since an entity arises only depending on its conditions, it lacks independent existence and intrinsic nature – it is empty. One can achieve philosophical enlightenment when she realizes the truth of emptiness.

All the schools in Mahayana traditions accept the truth of emptiness in one way or another. The debate on sudden/gradual enlightenment took place in Zen traditions, which belong to Mahayana traditions. But Zen masters would not recognize philosophical enlightenment as the ultimate awakening. For, philosophical enlightenment relies on the verbal/conceptual approach to the truth of emptiness, but Zen traditions deny the ultimate success of this conceptual approach.^[5] Zen masters also accept the philosophical truth of emptiness. Accordingly, they in fact recognize the existence of philosophical enlightenment. But they accept philosophical enlightenment only as a second-rate enlightenment that does not bring us the ultimate awakening that Zen traditions claim to provide.

The sudden/gradual debate on enlightenment has attracted much attention among East Asian Buddhists for more than a millennium. But I believe we still can shed new light on this issue if we further analyze the concepts of enlightenment and sudden. Now that we have considered the first kind of enlightenment above, we can discuss the issue of the sudden/gradual debate with regard to this philosophical version of enlightenment. Is philosophical enlightenment achieved all at once (suddenly, 頓悟) or only gradually (漸悟)? To answer this question, I suggest we first try to see if philosophical enlightenment has both quantitative and qualitative aspects. As will be shown below, our answer to the given question will vary depending on different aspects of philosophical enlightenment.

Let us first examine if philosophical enlightenment has a quantitative aspect such that it allows for different degrees of realization of the truth of emptiness, which is the truth of non-self and dependent arising. Does the enlightenment of this truth take place gradually step by step, or only all at once? There is no simple and straightforward answer to this question. To see the complexity of this problem, consider how we come to comprehend the philosophical truth of non-self and dependent arising. No one can achieve philosophical enlightenment without some serious preliminary studies of these philosophical concepts. One may well require a high school diploma or a college-level education to clearly understand the Buddhist claim of emptiness — the truth of non-self and dependent arising. And we are well aware that students typically spend several years to complete any decent level of their education. In this regard, sudden or instantaneous philosophical enlightenment seems to be out of the question. Consider the following example to see why it is not possible.

Imagine a college classroom where a professor is about to introduce students to the Buddha’s philosophical view of non-self and dependent arising and its Mahayanist version of emptiness. Those who are fresh from high school are, let us say, only 50% ready to understand these philosophical views. Other students might have already taken a couple of philosophy classes in college, and they are, say, 75% ready. Those transfer students who have taken a Buddhist philosophy class elsewhere may be 95% ready to fully comprehend the truth of emptiness. These different degrees of readiness to achieve philosophical enlightenment are, I believe, evidence that there is no sudden philosophical enlightenment. No one can understand calculus all at once without understanding arithmetic, algebra, and other areas of simpler mathematics. Likewise, no one can suddenly realize the truth of non-self and dependent arising and achieve philosophical enlightenment without a preliminary understanding of simpler philosophical concepts such as person, essence, self, dependence, condition, existence, non-existence, etc.

I am not denying the existence of some specific moments when we come to understand very clearly the truth of non-self and dependent arising. These ‘aha’ moments may well be called moments of philosophical enlightenment. We could feel that these moments come to us suddenly, naturally, and spontaneously. However, I suspect what might happen suddenly is only the given person’s awareness, that is, her occurrent recognition of her philosophical enlightenment, not the entire process of achieving philosophical enlightenment. Let me explain this point with an example. A student earns her bachelor’s degree at the moment when she receives her diploma at her commencement. But her degree was not achieved suddenly, instantaneously, or spontaneously at that moment. She needed to spend years working hard to complete coursework and satisfy all the other requirements for her degree. The entire degree-completing process takes several years. Neither an academic degree nor philosophical enlightenment may be achieved suddenly, all at once.

Let us return to the college classroom where the professor has completed her introduction of the Buddhist truth of non-self and dependent arising. Suppose most students have successfully understood and realized the truth of these two teachings. It would still be extremely rare, however, for us to encounter a student who could immediately begin to interpret everything about herself and the world conscientiously and thoroughly following these teachings of the Buddha. People simply require more time, often a lot of time, to apply these metaphysical truths comprehensively to all the various issues about themselves and the world. Most people would at first be quite overwhelmed with this tremendous task. The sudden actual application of the philosophical contents of this enlightenment is not possible.

Perhaps a very intelligent robot or android — someone like Commander Data in Star Trek: The Next Generation — can make an exception to both sudden philosophical enlightenment and the sudden actual application of its philosophical contents. Suppose the android was originally programmed with our usual and commonsensical views of self and the world. The android ‘believes’ in its permanent and immutable self and the independent existence and intrinsic natures of things in the world. According to the Buddha, these are the ordinary erroneous views of people that cause suffering in their lives. If this android should be reset and re-programmed with the Buddhist metaphysics of non-self and dependent arising, it would be philosophical enlightenment achieved all at once. In this way, the android may easily obtain sudden philosophical enlightenment. Also, the android would not require any chunk of time to begin to apply the new perspective of non-self and dependent arising to itself and everything else in the world. The sudden application of the philosophical contents of this enlightenment is also possible. As all of us would agree, however, the human brain and human psychology do not function this way. Sudden philosophical enlightenment and the sudden application of its philosophical contents may be possible for androids, but neither is available to humans. Humans, as the biological entities we are, simply require more time.

2. How to interpret the concept of sudden (頓)

Sudden philosophical enlightenment is out of the question for us because philosophical enlightenment allows for degrees of its achievement. This enlightenment is only gradually achieved.^[6] However, does philosophical enlightenment require a qualitative or logical change in one’s perspective of self and everything else in the world? Yes, it does. Philosophical enlightenment would not be possible without adopting a new way of viewing one’s own self and the world. This new perspective must include a radical/logical change in one’s belief system. For one thing, it is our popular and time-honored belief that we are persons with our own identities. Self is the referent of the word “I,” and it is something that makes a given person the person she is. Most people in the Western Hemisphere would identify self with soul. However, Buddhists deny the existence of self. They have a radically different view of our mode of existence. For example, Buddhists — especially Mahayana Buddhists — understand the nature of things in the world only in terms of their changes and relations to other things. They do not recognize any intrinsic nature of any entity because any entity arises only depending on its conditions and thereby lacks independent existence and self-nature (自性). This view of emptiness is radically different from the commonsensical understanding of the nature of things we encounter in the world. Philosophical enlightenment is achieved only when one changes her perspective of self and the world in a revolutionarily different way.^[7]

If the “sudden” in “sudden enlightenment” means a radical and dramatic qualitative/logical change in one’s perspective of self and everything else in the world,^[8] I believe that it must be admitted that philosophical enlightenment is always sudden enlightenment. Philosophically enlightened ones have views of self and the world that are from a logical point of view radically different from their previous perspectives. Philosophically enlightened ones now believe in non-self and dependent arising. They see everything as empty of intrinsic nature. Since the realization of this truth changes their understanding and interpretation of self and the world quite dramatically, it must be as good as to live a revolutionarily different life. Imagine what it must have been like for an astronomer in the 16th Century to begin to see the universe through Copernicus’ heliocentric system after spending most of his life believing in the geocentric system of Ptolemy. This change of astronomical perspective must have been quite a shocking event to this astronomer. Sudden philosophical enlightenment should be no less dramatic to us. After all, we have lived with firm belief in the existence of self and the intrinsic natures of things, but we now need to see that both self and everything else in the world are all empty of self-nature. What a radical change!

From a logical point of view, philosophical enlightenment is always sudden enlightenment. For it requires a radical, qualitative change in one’s perspective of self and the world. The truth of non-self and dependent arising — the truth of emptiness — is in principle (logically) applied to everything that there is. In this regard, there is no partial or gradual philosophical enlightenment. The same example I used above will help explain this point. When the heliocentric system replaced the geocentric system, it was quite a radical and revolutionary change. When the change of perspective happened, though, the change was from a logical point of view completed all at once and nothing more was left to be done. It was not the case that the heliocentric system was applied to the earth but not to Mars or Jupiter. The new system did not bring about a partial or gradual change to astronomy. The heliocentric system was theoretically/logically applied to every corner of the known universe without exception. Since this change was a logical change, its completion was absolutely comprehensive, instantaneous, and simultaneous. It was a sudden (頓) change. We can say exactly the same about philosophical enlightenment. The truth of non-self and dependent arising applies logically to everything in the world all at once, instantaneously, and simultaneously — suddenly! This radical, fundamental, revolutionary, and logical change does not allow for any partial or gradual change.

From an empirical point of view, however, this kind of sudden enlightenment — a radical change of one’s perspective — cannot take place instantaneously. Philosophical enlightenment is an empirical process, too. Water needs to be heated for a while to reach its boiling point. Students require several years of study to receive their diplomas. Taking months or years, Buddhists must study and understand basic philosophical concepts such as person, existence, causation, essence, etc. to realize the truth of non-self and dependent arising. These are all empirical processes that take place in our natural world. No such an empirical process can take place in an instant or all at once. Any claim of sudden enlightenment, if it is argued for from an empirical point of view, goes against our understanding that causal processes involve intermediary stages and temporal durations. If one claims that she has experienced enlightenment all of a sudden, it is, again, only her experience at a specific moment that might have felt sudden. The entire empirical process of enlightenment can never be sudden.

Let us wrap up our discussion before we move on to a different kind of enlightenment and its possibility of sudden enlightenment. From a logical point of view, philosophical enlightenment is always sudden enlightenment which requires a radical, qualitative change in one’s own perspective of self and the world. Empirically and quantitatively, however, philosophical enlightenment proceeds only as gradual enlightenment.

3. Nirvanic enlightenment and sudden enlightenment

I argue in “Chapter 4 Concepts of Enlightenment” that the concept of enlightenment has been extended to include some non-epistemic elements. All the Buddhas — all the enlightened ones — are free from suffering. They always remain in nirvana with or without remainder. They are not just philosophically enlightened. They have also cultivated their moral and spiritual characters so much as to be able to constantly remain in nirvana. Enlightened ones are no longer recognized as enlightened unless they can continuously remain in nirvana. This is the way we have come to understand the meaning of the word “The Buddha,” although its literal meaning is ‘The (Philosophically) Enlightened One.’ We believe, and in fact we require, that enlightened ones should always be able to remain in nirvana. I call this kind of enlightenment nirvanic enlightenment.

Attaining philosophical enlightenment itself does not necessarily make the enlightened ones achieve nirvana. Philosophical enlightenment is fundamentally a realization of the way things are in the world. It is enlightenment about the facts of the world. Nirvanic enlightenment is, however, about the way we should cultivate our moral and spiritual characters. This enlightenment is related to the way we ought to act in order to stay free from suffering and to remain in nirvana. The difference between the two kinds of enlightenment is well confirmed in our ordinary experiences. There are many intelligent people — intelligent enough to fully grasp the truth of non-self and dependent arising — but who have uncontrollable craving for money, power, and other worldly pleasures and cannot escape from the constant suffering brought about by this craving. They might be able to achieve philosophical enlightenment, but they cannot attain nirvanic enlightenment. Philosophical enlightenment and nirvanic enlightenment belong to two different logical dimensions. Accordingly, the sudden/gradual debate on nirvanic enlightenment may not be appropriately understood in light of the sudden/gradual debate on philosophical enlightenment. We need to start our discussion of the sudden/gradual debate afresh with this new type of enlightenment.

Nirvanic enlightenment does not have much to do with the logical nature of our perspectives on self and other entities in the world; it is not about the sudden, radical change of perspectives. This different type of enlightenment may be achieved only through the moral and spiritual cultivation of character. For instance, Buddhists are required to follow the Buddha’s eight right paths and cultivate wisdom, morality, and meditation. These paths will lead one to eliminate craving and, along with it, suffering. This cultivation of moral and spiritual character is an empirical process, and its achievement takes time. A sudden enlightenment of a logical nature may help Buddhists follow the eight paths with more ease, but if we once consider the empirical aspect of the process of nirvanic enlightenment, possible debate on sudden/gradual nirvanic enlightenment would not attract much attention. Nirvanic enlightenment, since it requires an empirical process, cannot be achieved all at once; it is always gradual enlightenment. Some may be able to change their psychology and develop new dispositions rather quickly, but most others require more time. People usually need to undergo slow processes of gradual change to come to form appropriate dispositions and develop virtues for nirvanic enlightenment. The pace of this change must depend on their education, temperaments, determination, social and natural environmental factors, etc. Well, some run fast, and others take more time to reach their destination. But what would be such a big deal about the little time difference as long as all of them can arrive at the same destination? Nirvanic enlightenment is achieved only gradually, and that is alright.^[9]Let us now ask the same question that we raised earlier in this chapter: Is enlightenment achieved gradually or all at once? A rather uninteresting but most reasonable answer would be: It depends on how we understand the concept of enlightenment. We have so far classified two different kinds of enlightenment — philosophical enlightenment and nirvanic enlightenment. Philosophical enlightenment has both quantitative and qualitative aspects. Since the quantitative aspect of philosophical enlightenment allows for degrees of the achievement of enlightenment, philosophical enlightenment is in this respect always gradual enlightenment. No sudden enlightenment is possible for us. But if we consider the logical/qualitative aspect of the new perspective on self and the world that this philosophical enlightenment brings about, the concept of sudden needs to be interpreted quite differently. “Sudden” in this respect should be understood as meaning ‘radical’ or ‘revolutionary’ as in ‘a radical/revolutionary change of paradigm’ in Kuhn’s sense. Philosophical enlightenment is always sudden enlightenment in its logical aspect. Finally, we have just seen that there is no sudden nirvanic enlightenment. Therefore, we must conclude that sudden enlightenment is possible only with respect to the logical/qualitative aspect of philosophical enlightenment.

4. Enlightenment in Zen traditions and sudden enlightenment

In “Chapter IV Concepts of Enlightenment,” I rejected the popular form of enlightenment advocated in the Zen traditions of East Asia as genuine enlightenment. Zen traditions typically require us to have some mysterious, ineffable experiences of awakening for us to be recognized as ultimately enlightened. These experiences are, however, fundamentally private experiences and they are in principle incommunicable. It is impossible to confirm objectively and publicly that anyone is truly enlightened in the way Zen traditions recognize.^[10] I have argued that contemporary philosophy should not accept this Zen enlightenment as a form of enlightenment.

In contrast with the difficulty of Zen enlightenment, there are many good ways for us to recognize someone as philosophically enlightened. For instance, a good length of this person’s philosophical discussion on the Buddhist view of non-self and dependent arising will clearly reveal to us if she is philosophically enlightened. Also, with regard to nirvanic enlightenment, if we observe for some good while the behavior patterns and emotional and other psychological traits of this person, we can almost always tell if she is really free from suffering. We do not in principle have insurmountable obstacles in recognizing a nirvanically enlightened one.

However, there is no way to publicly and objectively identify the existence of some particular mysterious private experience that is required for enlightenment in popular Zen traditions — precisely because it is supposed to be completely private and incommunicable. It is difficult to see how philosophers can accept this ‘private enlightenment’ as a kind of genuine enlightenment. Private enlightenment may well not be enlightenment at all.

One may think that if we cannot recognize as genuine enlightenment the popular form of enlightenment in Zen traditions there would be no point of discussing the sudden/gradual debate on Zen enlightenment. The sudden/gradual debate in Zen traditions, however, has always been an important issue in history. The majority of Zen schools have claimed for sudden enlightenment and ignored the path of gradual enlightenment. As I briefly noted above, many Zen traditions have accepted the view of Buddha Nature (佛性) and our original enlightenment (本覺), and they have argued that the enlightenment obtained in their ways is always sudden enlightenment. Their enlightenment is supposed to be comprehensively achieved all at once at the very moment when they realize, experience, and become one with Buddha-Nature. If one realizes the truth of the existence of this innate Buddhahood (本來佛) in herself, and if she experiences it and becomes one with it, she immediately gets enlightened. It is not just sudden enlightenment that these traditions have argued for. Since no Buddha requires any further moral or spiritual cultivation, the one who has newly realized her own innate Buddhahood has nothing left to cultivate. Hence, they claim for sudden enlightenment sudden cultivation (頓悟頓修). Although this view of Zen traditions has been influential in East Asian Buddhism, it faces a series of philosophical problems.

First, it is not clear if this ‘sudden’ enlightenment involves a radical change in one’s perspective on self and the world. Sudden enlightenment takes place when a given perspective, or a paradigm of belief system, is replaced with a revolutionarily different paradigm. The enlightened one should now see self and the world as entirely empty of intrinsic nature. She accepts the truth of non-self and dependent arising. She now views everything in the world differently, and “sudden” in “sudden enlightenment” describes a revolutionary change that takes place in her belief system. However, does such a radical change happen when one allegedly realizes her Buddha-Nature and becomes a Buddha herself? And if it does, is it what makes her enlightenment sudden enlightenment? I believe that there is no definite answer to this question. For so much of the view of these traditions is based on their faith in the existence of Buddha Nature. What makes our answer more difficult to give is that Zen traditions refuse to talk about the philosophical content of their enlightenment. The nature of Zen enlightenment has been said to be completely ineffable and incommunicable. Their enlightenment is presumed to be beyond the reach of philosophical enlightenment which is about a verbal and conceptual understanding of truth.

All in all, I believe it is only fair to admit that these Zen traditions do not really think of enlightenment as involving a revolutionary change in one’s perspective and belief system that are in principle verbally describable. They always play down the importance of philosophical enlightenment and often refuse to recognize it as enlightenment at all. We must conclude, from these considerations, that enlightenment in these Zen traditions cannot be sudden enlightenment where ‘sudden’ is understood to involve a radical change in perspective which can take place only with regard to philosophical enlightenment. If Zen enlightenment is enlightenment at all, therefore, it can only be gradual enlightenment. And if there is any specific moment when a practitioner feels a mysterious sensation of enlightenment, it may not be thought of as the moment of sudden enlightenment. The truth is only that she comes to experience that particular sensation at that specific moment. The entire process of intensive meditation that may lead to that specific moment of particular experience is often a very long and arduous journey. The enlightenment achieved this way needs to be regarded as gradual enlightenment, not sudden enlightenment.

Another problem of this view that involves the realization of Buddha-Nature is, as we discussed above with the problem of Zen enlightenment in general, the privacy of the enlightenment experience. As long as the realization of one’s innate Buddha-Nature is a private experience that is ineffable and incommunicable, there is no way we can confirm the existence of this experience objectively and publicly. Most philosophers would be reluctant to recognize this kind of private experience as evidence of enlightenment.

A more serious problem is, I believe, that the claim of the existence of Buddha-Nature and original enlightenment seems to be contradictory to the Buddha’s non-self, dependent arising, and emptiness. If everybody is fundamentally a Buddha, and if it takes only the realization of one’s innate Buddha-Nature to achieve enlightenment, how is this Buddha-Nature different from ātman (self) of Brahmanism? Brahmanism has also taught that one achieves her mokṣa (liberation) from all the suffering of transmigration when she realizes and identifies herself with ātman. But the Buddha famously denied the existence of ātman and presented his view of anātman (non-self). No school can be classified as a Buddhist school unless it accepts the Buddha’s teaching of non-self. Also, Buddha-Nature seems to be immutable and indestructible; it thereby defies the Buddhist thesis of impermanence and dependent arising. We must conclude that we should not accept the view of Buddha-Nature consistently with the basic teachings of the Buddha. If some Zen traditions base their claim of sudden enlightenment on this controversial view of Buddha-Nature, the credibility of their claim cannot but be seriously undermined.

Sudden enlightenment of these Zen traditions is supposed to be possible only by a private experience of Buddha Nature, whose existence is denied by the Buddha’s most basic teachings. I must conclude that we cannot accept Zen sudden enlightenment as genuine enlightenment.

5. Sudden enlightenment is possible only from a logical point of view

I have classified three different kinds of enlightenment: Philosophical enlightenment, nirvanic enlightenment, and enlightenment in Zen traditions. The Zen traditions require for their ultimate enlightenment an experience of some mysterious, private inner sensation. This essential privacy of their experience results in the ineffability and incommunicability of their enlightenment, and this impossibility of objective and public confirmation on Zen enlightenment presents serious problems for philosophers. From a philosophical point of view, it is hard to accept their enlightenment as a form of genuine enlightenment. Some Zen traditions have adopted the view of Buddha-Nature and original enlightenment and argued that their enlightenment is sudden enlightenment achieved by the realization of this innate Buddhahood. But it is difficult to accept the existence of this innate Buddha-Nature consistently with the fundamental teachings of the Buddha. With all these problems of the Zen enlightenment presented to us, we cannot expect to have a productive debate on the sudden/gradual enlightenment in Zen traditions.

Considering the two other kinds of enlightenment, nirvanic enlightenment, which is to be achieved through the moral and spiritual cultivation of character, is always gradual enlightenment. Philosophical enlightenment is fundamentally an epistemic achievement. Any epistemic achievement takes time. It cannot be obtained suddenly or all at once. However, the logical and qualitative aspect of philosophical enlightenment demands a replacement of one’s old belief system with the Buddhist perspective of non-self and dependent arising. This adoption of a new perspective is somewhat like a paradigm shift in one’s belief system. From a logical point of view, this involves a radical and revolutionary change in one’s own view of herself and the world. Since this change is logical in its nature, the change takes place all at once, altogether, simultaneously, and thoroughly comprehensively. In this regard, the logical aspect of philosophical enlightenment presents us a case of sudden enlightenment. Sudden enlightenment is philosophical enlightenment understood as a perspective change from a logical point of view.