Many people not raised as Buddhists have nonetheless heard of the Four Noble Truths. It is often the only central topic of Buddhism that they know: (1) suffering is the state of existence, (2) suffering is caused by desire, (3) the path to the cessation of suffering is the elimination of desire, and (4) that path is composed of eight components (the Eightfold Path). These truths are recorded in the Dhammacakkappavattana Sutta which is an account of the Buddha's first lecture following his enlightenment.
The Dhammacakkappavattana Sutta also recounts the Buddha's explanation of "dependent arising." Its place in his first lecture suggests that it is equally important to understanding the Buddha's teaching. Dependent arising is, however, a much more difficult concept. While the Four Noble Truths provide a clear and simple account of basic human psychology, dependent arising refers to a puzzling metaphyiscal view. On the surface, it describes a repeating sequence of changes to a person across successive reincarnated lives, but it also refers to the infinitely complex character of the objects of our experience, each moment in time. It was this latter, metaphysical account of dependent arising that most attracted me to a more serious study of Buddhism.
I had very little understanding of dependent arising until I read T.R.V. Murti's The Central Philosophy of Buddhism: A Study of the Madhymika System. Madhyamaka Buddhism was the first of the Mahayana Buddhist schools. It broke from early Buddhism by recognizing "new" sutras, not in the original Buddhist canon. The new sutras centered on two important ideas: the bodhisattva and sunyata (emptiness). I found that by understanding emptiness, the metaphysical aspect of dependent arising made much greater sense.
The first and possibly most authoritative explanation of emptiness was advanced by the Madhyamaka's founding author, Nagarjuna. Nagarjuna lived in the first and second century A.D. He is sometimes refered to as the second Buddha. His most import work, the Mulamadhyamakakarika sets up his account of emptiness by discussing a "tetralemma," which examines four possible states of affairs describing the basic facts of reality. (1) The fundamental elements of reality exist (existence). (2) The fundamental elements of reality don't exist (nihilism). (3) The fundamenatl elements of reality both exist and do not exist. (4) The fundamental elements of reality neither exist nor do not exist. Western logic tends to focus on only two ontological states: existence and non-existence. Consequently, it seems a little odd to expand the options to four, particularly when the additional two are built upon existence and non-existence, but there's no harm done by considering all four.
Nagarjuna examined each of these possibilities and concluded that none of them stood up to criticism. If that's true, then a clear understanding of reality is not possible, at least through rational investigation alone. To begin, we can easily dispense with possibilities (3) and (4). Consistent with Western analyses, (3) violates the Law of Noncontradiction: no statement and its negation can be true at the same time. (4) violates the Law of Excluded Middle: for any statement, either it or its negation must be true. This leaves us with options (1) or (2) as possibly describing the basic facts of reality.
We can dispense with (2) pretty quickly too. The simple fact of consciousness tells us that the non-existence of the world is untenable. Just as Descartes argued that thinking was sufficient to establish a thinker, consciousness establishes that there is some sort of reality. Indeed, the argument for the existence of the world seems more certain than Descartes's argument for the existence of a thinker. One might conclude then, that option (1) must be true, but Nagarjuna rejects (1) as well. By doing so, he establishes that all things we might posit as composing reality are "empty."
So let's turn from the tetralemma to emptiness. I understand the concept in two ways which I'll call "compositional" and "temporal." Regarding the composition of reality: what we take to be real is in fact constructed out of things that are ontologically more fundamental than what we perceive as real. Consider any ordinary object, say, a coffee cup. We think of it as an object, a thing, that exists in and of itself, but upon reflection informed by scientific examination, we know it not to be a thing, but instead, a collection of things -- atoms which in a sense are "more real" than any collection they might be a part of. After all, the collection can only exist dependently upon its components. We think of the atoms as having an existence in and of themselves, while the collection of atoms is just a lot of actual objects adhering in rather close proximity to one another.
But we should recognize that the atoms that compose the cup are themselves a collection of smaller objects and don't really exist in and of themselves. They are composed of protons, neutrons, and electrons. Furthermore, protons and neutrons are composed of smaller particles still. To get to what are the genuinely basic elements of the reality, we need to look deeper and deeper. Modern science postulates fundamental elements (elementary particles), but only if they are part of a good explanation of our experience. Currently, no physical theory can do that perfectly well. So elementary particles, like quarks, leptons, and gauge bosons, are our best guess at the foundations of the physical world. They are basically just practical conjectures.
Madhyamaka Buddhism holds that everything that we might consider to be an object existing in and of itself, no matter how small, is in fact a compilation of yet smaller objects. There are no elementary particles. As the joke goes, "it's turtles all the way down." Consequently, reality is not composed of anything that has permanent, independent existence. Instead, realtiy is an ephemeral construction of infinitely smaller and smaller elements. Reality, as we see it, is sunyata or "empty" of true existence.
It is quite reasonable to say that thinking that the world is composed of an infinite regress of smaller and smaller compound objects is a leap of faith. In all likelihood, it's a non-falsifiable claim. At the same time, it is also a leap of faith to say that reality is ultimately composed of elementary (uncuttable) particles. We simply are attracted to this atomist view because we are used to thinking about the objects around us which we now understand are collections of infered objects and don't exist in and of themselves. Upon closer reflection, there is no telling what the basic substructure of the universe is or if there even is a basic substructure.
This is how we understand emptiness through an examination of the composition of objects. We can also understand it temporally, through causal relationships. Without going into much detail, the Madhyamaka concept of emptiness is based also on the notion that no object can be said to be either completely separate from or joined with its causes or its effects. The temporal boundaries of apparent objects do not actually exist, despite the seemingly discrete existence of moments in time. Reality is not a sequence of distinct states of affairs. It is a smear of constant change, without objects in causal relations to one another. Ultimately, the world is one, ever changing, effervescent phenomenon. We cannot pin it down at any point in time and assert that what we have pinned down exists.
In short, Madhyamaka Buddhism asserts that there is no metaphysical theory that can conclusively establish anything as existing in and of itself, either compositionally or temporally. So a full analysis of the tetralemma tells us that each of the four possible states of reality cannot be confidently asserted. The examiniation of the tetralemma and the concept of emptiness leave us with a theoretical blank slate, upon which nothing can be written.
So how does this help us understand dependent arising? The answer is imbedded in those two words. "Arising" refers to the fact that a world is undeniably present to us. "Dependent" refers to its character as empty.
Madhyamaka Buddhists meditate on emptiness in order to become better disposed toward gaining enlightenment, i.e., freedom from delusion, desire (attraction), and hatred (aversion). These three "poisons" are the causes of suffering. Understanding that the world we experience is empty (devoid of objects that have an existence in and of themselves) holds the key to avoiding the delusions we naturally fall prey to. Reflecting on emptiness also mitigates our desires and our hatreds for any specific thing or state of affairs, since we recognize that the objects of our desires and hatreds do not inherently exist. This allows us to maintain a calm equinimity in difficult circumstances.
On a personal note, I have found that by meditating on emptiness, I am -- as the Madhyamika suggests -- able to cope much better with whatever trial I face. Additionally, the simple observation that my surroundings are rationally unintelligible and that they are in constant, effervescent flux, imbues the world with profound beauty. There's no wonder to me that dependent arising was among the Buddha's most fundamental teachings.