Brahmavihāra is a Buddhist term meaning "The Four Celestial Abiding States" or "The Four Immeasurables" (pali: appamaññā, skt.: apramana). The Brahmavihāras are the basis for meditation practices (brahmavihāra-bhāvanā) in Theravada as well as in Mahayana.
They are part of Buddhist ethics and denote four attitudes of mind toward other beings to be cultivated. Other translations of the term are: "The four immeasurable attitudes of mind," "The four limitless states of mind," "The four abodes of Brahma" (vihara means "abode," "place of abiding"; Brahma is an Indian deity).
Metta is an attitude of benevolence, a friendly unconditional affection that is not rooted in desire (attachment) and does not apply only to a few selected beings, but is motivated by interest in the happiness of all.
A benevolent recognition and appreciation of one's own person is the prerequisite for this form of unconditional loving ability. If this is not present, it can be learned.
Many Buddhist authors avoid translating metta as 'love', preferring instead terms such as "loving-kindness", "kindness" or "benevolence". The term 'love' is too strongly associated with possessive and greedy forms of passionate affection and easily leads to misunderstanding.
Karuna is compassion, the ability to deeply sympathize and empathize with other beings. In former times karuna was often translated as "compassion" and also in English today the term 'compassion' is still used here.
The term 'compassion', however, is misleading in that karuna does not require active compassion, and compassion always includes an element of condescension, of distancing oneself from the object being pitied. Empathy is also to be distinguished from sympathy, since it means feeling into other beings.
This form of empathy can lead to what is called "compassion fatigue," which is really "empathy fatigue." With empathy, we feel what the other person feels. With compassion, we feel WITH her/him.
The separation of subject and object, also found in compassion, contradicts the non-dualistic spirit of the Buddhist anatta teaching and the mindset of upeksha/upekkha - equanimity. Equanimity allows us to empathize without distancing ourselves or sinking into suffering ourselves.
While karuna is primarily about the ability to perceive the suffering of other beings, mudita is about sharing in the joy of other beings. mudita is co-joy, the gift of being able to share joyful (=suffering-free) moments with others.
This term has many levels of meaning: Equanimity, serenity, letting go, non-attachment, non-discrimination. In the meaning of equanimity, it refers to a form of serenity in relationships that acts as a corrective to the possessive and clinging tendencies of affection.
This equanimity is not to be confused with indifference. On another level of meaning, upeksha refers to insight into the fundamental equivalence of the objects of love and the fundamental equality between subject and object within the framework of metta.
"Four immensities: There radiates, brothers, a monk of loving mind, dwelling in one direction, then in a second, then in the third, then in the fourth, likewise upward and downward: recognizing himself everywhere in everything, he radiates through the whole world with loving mind, with wide, deep, unrestricted, cleared of anger and resentment. Being of a merciful mind, of a joyful mind, of an unmoved mind, he radiates in one direction, then in a second, then in the third, then in the fourth, likewise upward and downward: recognizing himself everywhere in everything, he radiates through the whole world with a merciful mind, with a joyful mind, with an unmoved mind, with a wide, deep, unrestricted mind, cleared of wrath and resentment."
- From the agreement