Samudaya

Samudaya is the Pali word for the second of The Four Noble Truths of Buddhism. It is the truth of the arising of dukkha.

Samudaya is most commonly referred to by the concept of tanha, or "thirst," as in desire, greed, volition, &c. Samudaya is not limited only to tanha, but it is unilaterally considered to be the primary cause. At its heart, tanha is the false idea of self that comes from ignorance.

When we thirst, it is for The Four Nutriments, those things that are responsible for existence and continuity.
These are:

1. Ordinary food
2. Contact by our mind and body with the outside world
3. Consciousness
4. Mental volition or will

It is the last of these that causes samudaya to be intimately tied to Buddhist views of karma. To be brief, Buddhists view tanha as the source of all volition in the universe. In the Buddhist view, karma is only generated by volitional acts. Thus, if a person lives without volition, they accumulate no karma. Volition is the most powerful force in all existence. When the physical body cannot support these energies, it dies, but the energy does not dissipate.

It is important to note that, as per Anatman, the Buddhist doctrine of no-soul, there is no permanent unchanging substance to pass from one life to the next; there is only change, only motion. Think of it this way: A child grows into a sixty-year-old man. The man is not the same as the child, but neither is he another person. So it is that when the man is reborn, he is neither the same person, nor another. This is samsara, or continuity.

Index of Noble Truth: Dukkha | Samudaya | Nirodha | Magga

Sources

Rahula, Walpola. What the Buddha Taught. New York: Grove Press. 1959.
Life