The teaching of the Twelve Causes and Conditions (dvadasanga-pratityasamutpada in Sanskrit) is the same as that of the Twelve-linked Chain of Dependent Origination. This is one of the teachings that form the core of basic Buddhism. In one of the sutras in the Dirgha-agama (Long Discourses), the Buddha explains this teaching in great detail to Ananda. In that text the Buddha teaches that there is a law of twelve stages of cause and effect in relation to the conception and development of the body (external dependent origination) as well as a law of twelve stages of cause and effect in regard to the development of the mind (internal dependent origination).
This teaching explains how people are born, mature physically, age, and die, tracing the causes and conditions of the process through the three worlds of past, present, and future. The Buddha goes on to explain that there is a similar principle of cause and effect in the evolution of our minds and teaches a fundamental method of purifying our minds and ridding ourselves of delusion.
The twelve stages in the process are (1) ignorance, (2) actions, (3) consciousness, (4) name and form, (5) the six sense organs, (6) contact, (7) sensation, (8) craving, (9) grasping, (10) becoming, (11) birth, and (12) old age and death. Let us look first at these phases in terms of the development and transmigration of the body.
Ignorance (avidya in Sanskrit) is written in Chinese with ideographs meaning "no light," or darkness, light being knowledge. The various kinds of karma that we have accumulated over the course of past lives lead us to repeat actions (samskara) whose fundamental cause is ignorance. These two steps belong to the world of the past. The spirit bearing such karma based on ignorance comes to reside in the mother's womb as a result of the parents' sexual activity.
When that spirit takes up residence in the womb, in other words, at the moment of conception, consciousness (vijnana) arises, though it is as yet incomplete. This is the true moment of birth; it is our entrance to the world of the present. As that incomplete consciousness gradually develops, it becomes name and form (nama-rupa). "Name" refers to the mind, in the sense of intangible, spiritual existence. "Form" - tangible, or physical, existence - refers to the body.
As name and form - that is, mind and body - further develop, they give rise to the six sense organs, or "six entrances" (sad-ayatana). These comprise the five sense organs-the eyes, ears, nose, tongue, and body (sense of touch)-plus the function of the mind that perceives the existence of things by means of these organs. Though the sense organs are ready to function, at this stage we are still in the womb and our perceptions are not clear. Some say that the term "entrances" is used because this is the stage at which the functions of body and mind "enter" the division of labor into six categories; others say the term refers to the sites at which external stimuli enter. Whatever the root meaning, this is the stage at which we are equipped with the six sense organs and they are prepared to function.
Now we leave the womb. The six sense organs are fully developed, and clearly defined sensations arise. We can distinguish forms, colors, sounds, smells, tastes, and various kinds of touch. This stage is called contact (sparsa). When we are able to perceive differences among things, feelings of like and dislike naturally arise. This is the stage of sensation (vedana). Sensation develops into craving (trsna). "Craving" has many meanings, but here it refers to the wish for the opposite sex. This in turn develops into grasping (upadana), that is, the desire to possess a person of the opposite sex. Marriage marks the stage of becoming (bhava). The natural result of marriage is children. The creation of this new life is the stage called birth (jati). For the parents, this new life represents their own rebirth in the future, so this stage marks the beginning of the world of the future. All who are born into this world, repeatedly experiencing grief, lamentation, suffering, and distress, finally reach the stage of old age and death (jara-marana). There ends the individual's life.
In this model, ignorance and actions belong to the past, all the stages from consciousness through becoming belong to the present, and birth and old age and death belong to the future. Since all three worlds are related to the past and the future as well as the present, the law of the Twelve-linked Chain of Dependent Origination is also called "cause and effect related to both sides of the three worlds."
Next let us discuss the Law of the Twelve Causes and Conditions with regard to the evolution of the mind (internal dependent origination). Again we begin with ignorance: not having the correct view of the world and of life, or ignoring it despite knowing it.
Because of ignorance, in the past we have acted in ways contrary to the truth (the universal law). That is the stage of actions, not only an individual's deeds but also the accumulation of all the experiences and all the deeds of humanity over its long history.
Consciousness is the most fundamental faculty by which human beings discern events and things. The manner in which this fundamental faculty operates is determined by past experiences and deeds - in other words, karma. Consciousness arises at the moment of conception, though at first it is an extremely vague and unfocused awareness.
As consciousness develops, it becomes name and form. As mentioned earlier, "name" refers to the mind, in the sense of intangible being, and "form" to tangible being, or the body. In other words, the stage of name and form is that at which the functions of mind and body start to develop and we first become aware of our own existence.
When name and form develop even further, the perceptions of the five sense organs - sight, hearing, smell, taste, and touch - and the faculty of the mind that discerns the existence of things perceived by the five sense organs become clearly defined. This is the stage of the six sense organs. Then we gain the ability to discern different people and things. This stage is called contact. When the mind has developed to this point, emotions arise, beginning with likes and dislikes and moving on to happiness, sadness, pleasure, and pain. This is the stage of sensation.
Once such emotions arise, craving for things, or attachment to them, is a natural result. We develop a liking for certain things and grow attached to them; in other words, our minds are captured by things that we like. Accordingly, we grasp at what we like and refuse to let go. Conversely, we flee from what we dislike. This state of mind is called grasping.
With grasping, various emotions, ideas, and opinions are generated. This process is called becoming, which refers to distinction, or making false distinctions between things. Distinction causes opposition and strife, and so our miserable, painful lives develop. Such human life is known as birth. In the course of this painful life, we age and, eventually, die. This is the stage of old age and death.
The sufferings of our lives are generated in this fashion. And their ultimate cause is the ignorance at the root of the process. All suffering is caused by not knowing or by ignoring the Law that is applicable to all things (the universal truth), the correct view of the world and of life.
If only we can rid ourselves of this ignorance and recognize the truth, our actions will also be correct. Each new mental act will correspond to the truth, and friction and obstructions will disappear. Suffering will fade from our minds, and we will be able to achieve peace of mind. This is the conclusion to which this teaching draws us.
When we consider our complete mental and physical existence in the light of the teaching of the Twelve-linked Chain of Dependent Origination, we realize that we were born as ordinary human beings because of ignorance in our previous life. But if, in the present life, we can correctly discern all things, freed of ignorance and informed with the wisdom of the Buddha, and then accumulate correct deeds (karma), we will eventually be able to escape from transmigration and become buddhas.