The Theory of Karma

Now, the Pali word kamma or the Sanskrit word karma (from the root kr to do) literally means 'actions', 'doing'. But in the Buddhist theory of karma it has a specific meaning: it means only 'volitional action', not all action. Nor does it mean the result of karma as many people wrongly and loosely use it. In Buddhist terminology karma never means its effect; its effect is known as the 'fruit' or the 'result' of karma (kamma-phala or kamma-vipaka).

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The Theory of karma should not be confused with so-called 'moral justice' or 'reward and punishment'. The idea of moral justice, or reward and punishment, arises out of the conception of a supreme being, a God, who sits in judgment, who is a law-giver and who decides what is right and wrong. The term 'justice' is ambiguous and dangerous, and in its name more harm than good is done to humanity. The theory of karma is the theory of cause and effect, of action and reaction; it is a natural law, which has nothing to do with the idea of justice or reward and punishment. Every volitional action produces its effects or results. If a good action produces good effects and a bad action bad effects, it is not justice, or reward, or punishment meted out by anybody or any power sitting in judgment on your action, but this is in virtue of its own nature, its own law.

---What the Buddha Taught, by Walpola Rahula---