Teachers in Buddhist traditions remind you that there is a principle you have to follow when you do the work of investigations. They said you shouldn't mix up the phenomenal and the noumenal. In the phenomenal, on the side of the level of the phenomenal, you use concepts, words and descriptions that you can not use in the approach of the noumenal. And this is the Buddhist principle of the investigation. It's called the separate investigation of the phenomenal and the noumenal. The phenomenal is a thing (luxana?) and the noumenal is a nature. This (The noumenal) is in the realm of ontology. This (The noumenal) is the ontological approach to the reality. This (The phenomenal) is the phenomenological approach to the reality. And you can not mix up the two kinds of methods. This is somehow like a classical science and a modern science. The notion of methods you apply to the classical science you have to leave behind if you want to succeed in approaching in the realm of a quantum physics. If you can't leave behind that, you have no hope in order to get into the realm of quantum physics and understand. And this is written in Chinese (?). (?) means "to investigate", "to study", "to learn", "to look deeply" and (?) means "separately". This is noumenal and this is phenomenal. This is ontological and this is phenomenal. When you want to approach the reality ontologically, you have to leave behind all these notions, ideas and words that you use while you investigate the phenomenal world.
And this is very important in Buddhism because Buddhism distinguish two kinds of truth, the conventional truth and the ultimate truth. In the conventional realm of truth, you can stick of birth and death, being and non-being, you and I, time and space as a separate entity. And you can apply that kind of knowledge into technology and into your daily life also. For instance, every one of us needs a birth certificate in order to have an identification card and a passport, or you can't go anywhere. You can't say that my nature is no birth and no death, so I don't need a birth certificate. You see? So, this kind of conventional truth does help. Yeah! In the ultimate truth, we know that it's impossible for a cloud to die. The cloud can't pass from the realm of being to the realm of non-being. That is the ultimate truth. But when someone dies, we have to declare that he has died. You can not say that he can never die and he is like a cloud. So, I don't need to declare his death. You can't do that. So, in the conventional truth, we make use of notions of birth and death, being and non-being. You and I are different. Father and son are two distinct persons. You can not mix up. Although in the ultimate truth, you can see the father in the son. If you remove the father from the son, he can no longer be there. So, you have to separate. You have to practice according to the separate investigation of the phenomenal and the noumenal, the ontological and the phenomenological.
And I think something similar should be observed inside. When you leave a domain in classical science, you have to be freer of notions and concepts in order to be able to approach. Because the quantum physics has the willingness to knock at the door of ontology. They try to find out what is the real sufferings of reality. The separate investigation of the phenomenal and the noumenal. So, when you speak of God, you speak of nirvana, you speak of the ultimate, you should use a kind of language that is different. You should no longer use the notions. And the words that you use when you speak of other things like the notion of being and non-being, you can not use it in order to describe God. So, the problem, whether God is or God is not, God exists or does not exist, is no longer a problem. The ultimate is free from the notion of being and non-being, birth and death. So, if we follow that, we can save a lot of time. We can save a lot of ink. And we can save a lot of saliva also.
I think in the domain of science, many scientists make that kind of mistakes. And in Buddhism also, even teachers make that kind of mistakes. They mix up two dimensions of reality. When you speak of the Four Noble Truths, for instance, we know that the first one is ill-being. And the second is the making of ill-being. The third is the secession of ill-being. And the fourth is the path leading to the secession of ill-being. And there are Buddhist teachers who describe the third noble truth, nirvana, in terms of the ultimate. And they say among the four truths, one belongs to the ultimate and three others belong to the conventional. And such teachers don't observe the non-separate investigation of truths. There are more than one teachers who explain the Four Noble Truths like that. And if we follow the principle, the methodology we know, that is not correct. If we stay in the realm of the conventional truth, you have to say that all four of them are conventional. All of them are Sanskrit terms of Dharma, conditioned Dharma. Suffering is conditioned. Suffering is made of non-suffering elements. Suffering manifests because many conditions come together in order to help suffering manifest. And that is the second noble truth. How elements come together to produce suffering we have to look deeply. So, the first and the second noble truths we have to examine in the level of conventional truths.
And the path leading to the secession of ill-being, the path for transformation and healing, the path that can disgrace ill-being with well-being, should be seen in the realm of conventional truth. Because everything is impermanent, suffering is impermanent and the secession of suffering is impermanent also. The secession of suffering means happiness. And happiness is as impermanent as suffering. Because in the realm of conventional truth, everything is impermanent, is changing. So, you should not be right to single out the third and say that this is a non-conditioned Dharma and all the others are conditioned Dharma. You mix up the two things.
But when you read the Heart Sutra, you touch the ultimate dimension. And they speak of the Four Noble Truths in the language of the ultimate. They say there is no suffering, there is no making of suffering, there is no secession of suffering, there is no path leading to secession of suffering. That's the ultimate. So, if it is conventional, all four of them are conventional. If it is the ultimate, all of them should be ultimate. In the ultimate dimension, we say that ill-being doesn't exist as a separate entity. Without the three others, ill-being can not express itself. And that is why looking at the Four Noble Truths with the insight of interbeing, there can not be ill-being if there is no well-being. Because ill-being and well-being are related to each other. It is with the materials of ill-being that you can fabricate well-being and etc. It is with the mud that you can fabricate lotus flowers. So, both mud and the lotus are on the same level. They are all conditioned Dharma.
But if we single out the third truth and call it unconditional Dharma that is nirvana, we mix up and make confusion. That is why our Dharma teachers in Plum Village, whether they are monastics or lay, know that the third truth is linked with the first one. The first one is the presence of ill-being and the third one is the secession of the ill-being. It means the presence of well-being. Both ill-being and well-being are impermanent. They can change. That is why on this level the same happiness is impermanent. I have to continue my practice so that when happiness regenerates into something less than happiness, I can recreate happiness. You see? You can not say this is nirvana that is unconditioned. This is very important.
But the unconditioned is hidden behind. If you touch that conditioned Dharma deeply enough, you touch the unconditioned. And you don't have to look for the unconditioned elsewhere. It's like a cloud in the sky. Touching the cloud superficially, you see the cloud can be or can not be, the cloud can be born or can die. And you see the existence of the cloud or the non-existence of the cloud. you see the birth of the cloud or the dying of the cloud. So, that cloud belongs to the realm of conditioned dharma when we describe the cloud in terms of being there or not being there, or birth and death. As far as we stay in the realm of the conventional truth, it's okay, alright to use being and non-being, birth and death of a cloud.
But when you want to go deeper, you want to investigate deeper the same cloud, you touch more deeply and you find out it's impossible for a cloud to be born or to die. The cloud is free from birth and death, from being and non-being. And the ultimate is not something separated from the conventional. You don't have to throw away the cloud in order to obtain its true nature. You just touch it more deeply by removing all notions that you have of it before and then you touch the unconditioned. So, the unconditioned, nirvana, the ultimate is not something separated. It's like a wave suffer from going up and down, is afraid of being there or not being there, of being higher or lower than other clouds (waves?). So, that kind of sufferings are due to concepts, to notions and discrimination. But once the wave recognizes she is water and then she loses all these kinds of concepts, she loses all kinds of fear, anger and jealousy. That is why going up she is happy, going down she is happy. She is free from the notions of being and non-being, beginning and ending. And she doesn't have to go out to look for water. She is water. So, the ultimate is in the conventional.
We have to follow the principle of the investigation, the separate investigation of the phenomenal (the historical dimension) and the noumenal (the ultimate dimension). But the ultimate dimension is inside of the historical dimension.
Thích Nhất Hạnh