Causes of Reincarnation

I think there are two main reasons "why," which is the question. First, according to the Pali Canon the Buddha actually experienced past life memories as a result of his Enlightenment experience. Second, the law of karma requires that every cause have an effect; therefore, if at death there are any "unfruited" causes, as will be the case with anyone driven by desirous attachment, these must remanifest in a subsequent rebirth, even if there is no permanent self or "soul."

The Buddha's most famous sutta about "not-self" is the Anatta-lakkhana Sutta (SN 22.59).

There are various things (called Skandhas) which you might (mistakenly) think of as self:

• Form (matter or body)
• Sensation (feeling)
• Perception
• Mental formations
• Consciousness

The Buddha argues that these are all impermanent, and not under our control, so we shouldn't think of them as self: we shouldn't think, for example, "I am this body" nor "I have this body"; and similarly for sensation, consciousness, etc.

Because there's nothing that isn't impermanent, there's nothing that can be described as self (or as soul).

Another sutta is Alagaddupama Sutta (MN 22), which includes the following:

22. "You may well take hold of a possession,[26] O monks, that is permanent, stable, eternal, immutable, that abides eternally the same in its very condition. (But) do you see, monks, any such possession?" — "No, Lord." — "Well, monks, I, too, do not see any such possession that is permanent, stable, eternal, immutable, that abides eternally the same in its very condition."

23. "You may well accept, monks, the assumption of a self-theory[27] from the acceptance of which there would not arise sorrow and lamentation, pain, grief, and despair. (But) do you see, monks, any such assumption of a self-theory?" — "No, Lord." — "Well, monks, I, too, do not see any such assumption of a self-theory from the acceptance of which there would not arise sorrow and lamentation, pain, grief and despair."

In the above verses he says that if you can find something that's permanent, which if you accept it doesn't lead to "sorrow and lamentation, pain, grief, and despair", then you may accept it.

But, he doesn't see anything like that, and therefore doesn't assume there is such a thing (a thing which you should view, which you would be wise to view, as permanent self, permanently yours, e.g. "soul").

40. "Therefore, monks, give up whatever is not yours.[45] Your giving it up will for a long time bring you welfare and happiness. What is it that is not yours? Corporeality is not yours. Give it up! Your giving it up will for a long time bring you welfare and happiness. Feeling is not yours. Give it up! Your giving it up will for a long bring you welfare and happiness. Perception is not yours. Give it up! Your giving it up will for a long time bring you welfare and happiness. Mental formations are not yours. Give them up! Your giving them up will for a long time bring you welfare and happiness. Consciousness is not yours. Give it up! Your giving it up will for a long time bring you welfare and happiness.

The above verse is maybe part of the general Buddhist advice, that being attached to (or desiring) impermanent things results in unhappiness.

If Buddha didn't believe in soul why did he believe in Re-incarnation, after life etc which could be because of soul?

So apparently he didn't believe in soul because he saw things (everything) as impermanent.

There are various reasons for believing in rebirth: but one of them might be not seeing death as permanent. Someone once wrote, "Buddhists don't believe in death".

Actually the same person wrote that Buddhists (at least, Theravada Buddhists ... Tibetan Buddhism explains things differently) don't believe in reincarnation, they believe in rebirth. And really it's more just a believe in "birth" (as a cause of suffering and existence), rather than rebirth.

Another reason, I think, was because it's important to teach that actions and intentions have moral (as well as material) consequences.

Also, by the way, there's the matter of other people and of altruism. Assuming that actions are inconsequential would be wrong, according to AN 10.176:

And how is one made impure in three ways by mental action? There is the case where a certain person is covetous. He covets the belongings of others, thinking, 'O, that what belongs to others would be mine!' He bears ill will, corrupt in the resolves of his heart: 'May these beings be killed or cut apart or crushed or destroyed, or may they not exist at all!' He has wrong view, is warped in the way he sees things: 'There is nothing given, nothing offered, nothing sacrificed. There is no fruit or result of good or bad actions. There is no this world, no next world, no mother, no father, no spontaneously reborn beings; no brahmans or contemplatives who, faring rightly & practicing rightly, proclaim this world & the next after having directly known & realized it for themselves.' This is how one is made impure in three ways by mental action.

Some teachers like the Dalai Lama say that it's by seeing other people as important that he doesn't feel trapped (which he would feel, trapped, if he thought of himself).

Another way to answer this question would be to say that the "cause" is karma, craving, and/or (in more detail) the 12 nidanas.

The Pali scriptures (e.g. SN 12.2) define the word 'jati' ('birth') to mean the mental generation of the view, idea or thought concept of 'beings' ('satta') or 'self'. Please also refer to SN 5.10.

For example, in India today, the word 'jati' means 'social-self identity' or 'caste' rather than child birth from a woman's womb. To quote Wikipedia:

Jāti (in Devanagari: जाति, Bengali: জাতি, Telugu:జాతి, Kannada:ಜಾತಿ, Malayalam: ജാതി, Tamil:ஜாதி, literally "birth") is a group of clans, tribes, communities and sub-communities, and religions in India. Each jāti typically has an association with a traditional job function or tribe. Religious beliefs (e.g. Sri Vaishnavism or Veera Shaivism) or linguistic groupings may define some jatis. Among the Muslims, the equivalent category is Qom or Biradri.

A person's surname typically reflects a community (jati) association: thus Gandhi = perfume seller, Dhobi = washerman, Srivastava = military scribe, etc. In any given location in India 500 or more jatis may co-exist, although the exact composition will differ from district to district.

This contemporary Indian meaning of the word 'jati' is also found in ancient Pali scriptures, such as MN 98 (which describes the various social designations or 'jati' of people based on their kamma) and MN 86 (which refers to the life of a monk as a 'noble birth').

Therefore, what is called 'rebirth' in the Pali scriptures is the re-arising of this 'self-view' or 'self-social identity' within the mind (rather than reincarnation from life-to-life).

This 'rebirth' is caused ignorance & craving. Due to kamma (action), the mind develops more craving &, due to ignorance, the mind clings to that craving as 'self' or 'me'. This is 'rebirth'.

The famous Buddhist monk Ajahn Sumedho said:

Or, we speculate about re-birth: what is it that carries on from one life to the next if there's no soul? If everything's anatta, how can 'I' have been something in a previous life and have some essence that is born again?

But if you watch the way things operate independently of yourself, you begin to understand that rebirth is nothing more than desire seeking some object to absorb into, which will allow it to arise again. This is the habit of the heedless mind. When you get hungry, because of the way you've been conditioned, you go out and get something to eat. Now that's an actual rebirth: seeking something, being absorbed into that very thing itself. Rebirth is going on throughout the day and night, because when you get tired of being reborn you annihilate yourself in sleep. There's nothing more to it than that. It's what you can see. It's not a theory, but a way of examining and observing kammic actions.

Kamma & Rebirth

As for Krishna, his appearance in the Bhagavada Gita (composed around 200 BC) occurred after the Buddha therefore Krishna could not be a previous reincarnation of the Buddha. Such ideas are obvious Hindu rather than Buddhist because, in the Pali Buddhist scriptures, the only gods mentioned are Indra (Vishnu), Brahma & Prajapati.