The Buddha points to two mental qualities as the underlying safeguards of morality, thus as the protectors of both the individual and society as a whole. These two qualities are called in Pali hiri and ottappa. Hiri is an innate sense of shame over moral transgression; ottappa is moral dread, fear of the results of wrongdoing. The Buddha calls these two states the bright guardians of the world (sukka lokapala). He gives them this designation because as long as these two states prevail in people's hearts the moral standards of the world remain intact, while when their influence wanes the human world falls into unabashed promiscuity and violence, becoming almost indistinguishable from the animal realm (Itiv. 42).
While moral shame and fear of wrongdoing are united in the common task of protecting the mind from moral defilement, they differ in their individual characteristics and modes of operation. Hiri, the sense of shame, has an internal reference; it is rooted in self-respect and induces us to shrink from wrongdoing out of a feeling of personal honor. Ottappa, fear of wrongdoing, has an external orientation. It is the voice of conscience that warns us of the dire consequences of moral transgression: blame and punishment by others, the painful kammic results of evil deeds, the impediment to our desire for liberation from suffering. Acariya Buddhaghosa illustrates the difference between the two with the simile of an iron rod smeared with excrement at one end and heated to a glow at the other end: hiri is like one's disgust at grabbing the rod in the place where it is smeared with excrement, ottappa is like one's fear of grabbing it in the place where it is red hot.
In the present-day world, with its secularization of all values, such notions as shame and fear of wrong are bound to appear antiquated, relics from a puritanical past when superstition and dogma manacled our rights to uninhibited self-expression. Yet the Buddha's stress on the importance of hiri and ottappa was based on a deep insight into the different potentialities of human nature. He saw that the path to deliverance is a struggle against the current, and that if we are to unfold the mind's capacities for wisdom, purity and peace, then we need to keep the powderkeg of the defilements under the watchful eyes of diligent sentinels.