Yama, in the context of yoga or spiritual discipline, means a moral code of conduct, spiritual duty or observance to be followed. In Amarakosha, an ancient dictionary of Sanskrit terms, yamas are defined as the part of karma (everyday behavior) that must necessarily be nitya (performed daily), while niyama is that behavior which is casual, accidental or agantu (adventitious). It is stated in Manusmriti (IV.204) that if one follows only niyamas without yamas, one can fall from the spiritual path. So Yamas must be practiced without exception.
The number of yamas and niyamas are mentioned differently in different texts, and yama in one text may be mentioned as niyama in another text. The following ten yamas are mentioned in Darshana Upanishad (I.6) – non violence, truthfulness, non-acceptance of what really belongs to others as belonging to oneself, control of sex desire, being merciful to others, being straightforward in dealings, forbearance toward others, fortitude, moderation of diet, purification of body and mind. These same ten terms appear in other texts also.
We find ten yamas mentioned also in Yajnavalkya Smriti (III.312). That list includes only the first five yamas mentioned above. In place of the five yamas it includes last following five which are not found in the above list – patience, chastity, wholesomeness, sweetness, and control of sense organs.
In Mandala Brahmana Upanishad (I.1.3), only four yamas and nine niyamas are mentioned. The four yamas ad nine niyamas are mentioned. The four yamas are – ‘control of heat, cold, diet and sleep’, attitude of peace, undistributed stability in wake of experience and control of the senses.
Only five yamas and five niyamas are mentioned in the Yogasutra of Patanjali (II.30). Yamas are – non-violence, abandoning untruth, non-stealing, restraint and abstinence, and giving up accumulation of wealth and materials of enjoyment. The last yama in this list does not appear in any other text mentioned above. These last five yamas also appear in Vishnu Purana (VI.7.36).
The five yamas form anga (first part) of the eightfold yoga of Patanjali. They are the don’ts – that kind of behavior which is to be avoided by the aspirant. Niyamas on the other hand show what is to be positively done in daily life. If practice of yamas is continued without break for a long time, irrespective of birth in a parti, placecular caste, place, time or occasion, or exigency, then they attain the status of great vows ( Yoga Sutra II.31) and yield remarkable results.
With unbroken continuity yamas become an inseparable part of one’s very nature. This is called firm establishment of yama. When non-violence reaches that the state in the adept’s behavior, all creatures give up enmity his presence (II.35). With pratistha of satya the adept’s speech always comes true and events take place as he says (II.36). Non-stealing results in all gems approaching the adept (II.37). Unfailing energy is the result of brahmacharya (II.38). And finally, when the fifth yama is firmly established the adept knows the conditions of rebirth (II.39). In short, five yamas lead to five different yogic powers. Patanjali has further mentioned the siddhis (powers) attained by practice of five niyamas (II.40-45).
Natural inborn tendencies of the human mind are not favorable to the practice of yamas. They often tend to get an upper hand and hinder practice. Patanjali calls them vitarkas (distracting tendencies). He recommended a technique called pratipaksha bhavana (converse attitude) to curb them. Only then would morality of yamas become firmly established.