One of the fundamental views in Buddhism is the principle of "dependent origination." This states that all phenomena, both subjective experiences and external objects, come into existence in dependence upon causes and conditions; nothing comes into existence uncaused. Given this principle, it becomes crucial to understand what causality is and what types of cause there are. In Buddhist literature, two main categories of causation are mentioned: (i) external causes in the form of physical objects and events, and (ii) internal causes such as cognitive and mental events.

The reason for an understanding of causality being so important in Buddhist thought and practice is that it relates directly to sentient beings' feelings of pain and pleasure and the other experiences that dominate their lives, which arise not only from internal mechanisms but also from external causes and conditions. Therefore it is crucial to understand not only the internal workings of mental and cognitive causation but also their relationship to the external material world.

The fact that our inner experiences of pleasure and pain are in the nature of subjective mental and cognitive states is very obvious to us. But how those inner subjective events relate to external circumstances and the material world poses a critical problem. The question of whether there is an external physical reality independent of sentient beings' consciousness and mind has been extensively discussed by Buddhist thinkers. Naturally, there are divergent views on this issue among the various philosophical schools of thought. One such school [Cittamatra] asserts that there is no external reality, not even external objects, and that the material world we perceive is in essence merely a projection of our minds. From many points of view, this conclusion is rather extreme. Philosophically, and for that matter conceptually, it seems more coherent to maintain a position that accepts the reality not only of the subjective world of the mind, but also of the external objects of the physical world.

Now, if we examine the origins of our inner experiences and of external matter, we find that there is a fundamental uniformity in the nature of their existence in that both are governed by the principle of causality. Just as in the inner world of mental and cognitive events, every moment of experience comes from its preceding continuum and so on ad infinitum. Similarly, in the physical world every object and event must have a preceding continuum that serves as its cause, from which the present moment of external matter comes into existence.

In some Buddhist literature, we find that in terms of the origin of its continuum, the macroscopic world of our physical reality can be traced back finally to an original state in which all material particles are condensed into what are known as "space particles." If all the physical matter of our macroscopic universe can be traced to such an original state, the question then arises as to how these particles later interact with each other and evolve into a macroscopic world that can have direct bearing on sentient beings' inner experiences of pleasure and pain. To answer this, Buddhists turn to the doctrine of karma, the invisible workings of actions and their effects, which provides an explanation as to how these inanimate space particles evolve into various manifestations.

The invisible workings of actions, or karmic force (karma means action), are intimately linked to the motivation in the human mind that gives rise to these actions. Therefore an understanding of the nature of mind and its role is crucial to an understanding of human experience and the relationship between mind and matter. We can see from our own experience that our state of mind plays a major role in our day-to-day experience and physical and mental well-being. If a person has a calm and stable mind, this influences his or her attitude and behavior in relation to others. In other words, if someone remains in a state of mind that is calm, tranquil and peaceful, external surroundings or conditions can cause them only a limited disturbance. But it is extremely difficult for someone whose mental state is restless to be calm or joyful even when they are surrounded by the best facilities and the best of friends. This indicates that our mental attitude is a critical factor in determining our experience of joy and happiness, and thus also our good health.

To sum up, there are two reasons why it is important to understand the nature of mind. One is because there is an intimate connection between mind and karma. The other is that our state of mind plays a crucial role in our experience of happiness and suffering. If understanding the mind is very important, what then is mind, and what is its nature?

Buddhist literature, both sutra and tantra, contains extensive discussions on mind and its nature. Tantra, in particular, discusses the various levels of subtlety of mind and consciousness. The sutras do not talk much about the relationship between the various states of mind and their corresponding physiological states. Tantric literature, on the other hand, is replete with references to the various subtleties of the levels of consciousness and their relationship to such physiological states as the vital energy centers within the body, the energy channels, the energies that flow within these and so on. The tantras also explain how, by manipulating the various physiological factors through specific meditative yogic practices, one can effect various states of consciousness.

According to tantra, the ultimate nature of mind is essentially pure. This pristine nature is technically called "clear light." The various afflictive emotions such as desire, hatred and jealousy are products of conditioning. They are not intrinsic qualities of the mind because the mind can be cleansed of them. When this clear light nature of mind is veiled or inhibited from expressing its true essence by the conditioning of the afflictive emotions and thoughts, the person is said to be caught in the cycle of existence, samsara. But when, by applying appropriate meditative techniques and practices, the individual is able to fully experience this clear light nature of mind free from the influence and conditioning of the afflictive states, he or she is on the way to true liberation and full enlightenment.

Hence, from the Buddhist point of view, both bondage and true freedom depend on the varying states of this clear light mind, and the resultant state that meditators try to attain through the application of various meditative techniques is one in which this ultimate nature of mind fully manifests all its positive potential, enlightenment, or Buddhahood. An understanding of the clear light mind therefore becomes crucial in the context of spiritual endeavor.

In general, the mind can be defined as an entity that has the nature of mere experience, that is, "clarity and knowing." It is the knowing nature, or agency, that is called mind, and this is non-material. But within the category of mind there are also gross levels, such as our sensory perceptions, which cannot function or even come into being without depending on physical organs like our senses. And within the category of the sixth consciousness, the mental consciousness, there are various divisions, or types of mental consciousness that are heavily dependent upon the physiological basis, our brain, for their arising. These types of mind cannot be understood in isolation from their physiological bases.

Now a crucial question arises: How is it that these various types of cognitive events—the sensory perceptions, mental states and so forth—can exist and possess this nature of knowing, luminosity and clarity? According to the Buddhist science of mind, these cognitive events possess the nature of knowing because of the fundamental nature of clarity that underlies all cognitive events. This is what I described earlier as the mind's fundamental nature, the clear light nature of mind. Therefore, when various mental states are described in Buddhist literature, you will find discussions of the different types of conditions that give rise to cognitive events. For example, in the case of sensory perceptions, external objects serve as the objective, or causal condition; the immediately preceding moment of consciousness is the immediate condition; and the sense organ is the physiological or dominant condition. It is on the basis of the aggregation of these three conditions—causal, immediate and physiological—that experiences such as sensory perceptions occur.

Another distinctive feature of mind is that it has the capacity to observe itself. The issue of mind's ability to observe and examine itself has long been an important philosophical question. In general, there are different ways in which mind can observe itself. For instance, in the case of examining a past experience, such as things that happened yesterday you recall that experience and examine your memory of it, so the problem does not arise. But we also have experiences during which the observing mind becomes aware of itself while still engaged in its observed experience. Here, because both observing mind and observed mental states are present at the same time, we cannot explain the phenomenon of the mind becoming self-aware, being subject and object simultaneously, through appealing to the factor of time lapse.

Thus it is important to understand that when we talk about mind, we are talking about a highly intricate network of different mental events and states. Through the introspective properties of mind we can observe, for example, what specific thoughts are in our mind at a given moment, what objects our minds are holding, what kinds of intentions we have and so on. In a meditative state, for example, when you are meditating and cultivating a single- pointedness of mind, you constantly apply the introspective faculty to analyze whether or not your mental attention is single-pointedly focused on the object, whether there is any laxity involved, whether you are distracted and so forth. In this situation you are applying various mental factors and it is not as if a single mind were examining itself. Rather, you are applying various different types of mental factor to examine your mind.

As to the question of whether or not a single mental state can observe and examine itself, this has been a very important and difficult question in the Buddhist science of mind. Some Buddhist thinkers have maintained that there s a faculty of mind called "self- consciousness," or "self-awareness." It could be said that this is an apperceptive faculty of mind, one that can observe itself. But this contention has been disputed. Those who maintain that such an apperceptive faculty exists distinguish two aspects within the mental, or cognitive, event. One of these is external and object-oriented in the sense that there is a duality of subject and object, while the other is introspective in nature and it is this that enables the mind to observe itself. The existence of this apperceptive self-cognizing faculty of mind has been disputed, especially by the later Buddhist philosophical school of thought the Prasangika.

In our own day-to-day experiences we can observe that, especially on the gross level, our mind is interrelated with and dependent upon the physiological states off the body. Just as our state of mind, be it depressed or joyful, affects our physical health, so too does our physical state affect our mind.

As I mentioned earlier, Buddhist tantric literature mentions specific energy centers within the body that may, I think, have some connection with what some neurobiologists call the second brain, the immune system. These energy centers play a crucial role in increasing or decreasing the various emotional states within our mind. It is because of the intimate relationship between mind and body and the existence of these special physiological centers within our body that physical yoga exercises and the application of special meditative techniques aimed at training the mind can have positive effects on health. It has been shown, for example, that by applying appropriate meditative techniques, we can control our respiration and increase or decrease our body temperature.

Furthermore, just as we can apply various meditative techniques during the waking state so too, on the basis of understanding the subtle relationship between mind and body, can we practice various meditations while we are in dream states. The implication of the potential of such practices is that at a certain level it is possible to separate the gross levels of consciousness from gross physical states and arrive at a subtler level of mind and body. In other words, you can separate your mind from your coarse physical body. You could, for example, separate your mind from your body during sleep and do some extra work that you cannot do in your ordinary body. However, you might not get paid for it!

So you can see here the clear indication of a close link between body and mind: they can be complementary. In light of this, I am very glad to see that some scientists are undertaking significant research in the mind/body relationship and its implications for our understanding of the nature of mental and physical well-being. My old friend Dr. Benson [Herbert Benson, MD, Associate Professor of Medicine, Harvard Medical School], for example, has been carrying out experiments on Tibetan Buddhist meditators for some years now. Similar research work is also being undertaken in Czechoslovakia. Judging by our findings so far, I feel confident that there is still a great deal to be done in the future.

As the insights we gain from such research grow, there is no doubt that our understanding of mind and body, and also of physical and mental health, will be greatly enriched. Some modern scholars describe Buddhism not as a religion but as a science of mind, and there seem to be some grounds for this claim.