Indriya is the Sanskrit and Pali term for physical strength or ability in general, and for the senses more specifically. In Buddhism, the term refers to multiple intrapsychic processes and is generally translated as "faculty" or, in specific contexts, as "spiritual faculty" or "controlling principle." The term literally means "belonging to Indra," chief deity in the Rig Veda and lord of the Trāyastriṃśa heaven hence connoting supremacy, dominance and control, attested in the general meaning of "power, strength" from the Rig Veda. In Buddhism, depending on the context, indriya traditionally refers to one of the following groups of faculties:
In the Pali Canon's Sutta Pitaka, indriya is frequently encountered in the context of the "five spiritual faculties" : Together, this set of five faculties is one of the seven sets of qualities lauded by the Buddha as conducive to Enlightenment. SN 48.10 is one of several discourses that characterizes these spiritual faculties in the following manner: In SN 48.51, the Buddha declares that, of these five faculties, wisdom is the "chief".
Balancing the spiritual faculties
In AN 6.55, the Buddha counsels a discouraged monk, Sona, to balance or "tune" his spiritual faculties as one would a musical instrument: Relatedly, the Visuddhimagga and other post-canonical Pali commentaries caution against one spiritual faculty overpowering and inhibiting the other four faculties, and thus generally recommend modifying the overpowering faculty with the investigation of states or the development of tranquillity. Moreover, these commentaries especially recommend that the five spiritual faculties be developed in counterbalancing dyads:
"For one strong in faith and weak in understanding has confidence uncritically and groundlessly. One strong in understanding and weak in faith errs on the side of cunning and is as hard to cure as one sick of a disease caused by medicine. With the balancing of the two a man has confidence only when there are grounds for it."
"... dleness overpowers one strong in concentration and weak in energy, since concentration favours idleness. Agitation overpowers one strong in energy and weak in concentration, since energy favours agitation. But concentration coupled with energy cannot lapse into idleness, and energy coupled with concentration cannot lapse into agitation. So these two should be balanced ; for absorption comes with the balancing of the two."
"... One working on concentration needs strong faith, since it is with such faith and confidence that he reaches absorption."
"... Then there is concentration and understanding. One working on concentration needs strong unification, since that is how he reaches absorption; and one working on insight needs strong understanding, since that is how he reaches penetration of characteristics; but with the balancing of the two he reaches absorption as well."
"Strong mindfulness, however, is needed in all instances; for mindfulness protects the mind lapsing into agitation through faith, energy and understanding, which favour agitation, and from lapsing into idleness through concentration, which favours idleness.".
In SN 48.43, the Buddha declares that the five spiritual faculties are the Five Powers and vice versa. He uses the metaphor of a stream passing by a mid-stream island; the island creates two streams, but the streams can also be seen as one and the same. The Pali commentaries remark that these five qualities are "faculties" when used to control their spheres of influence, and are "powers" when unshakeable by opposing forces.
In the Sutta Pitaka, six sensory faculties are referenced in a manner similar to the six sense bases. These faculties consist of the five senses with the addition of "mind" or "thought". The first five of these faculties are sometimes referenced as the five material faculties.
22 phenomenological faculties
In the Abhidhamma Pitaka, the notion of indriya is expanded to the twenty-two "phenomenological faculties" or "controlling powers" which are:
At times in the Pali Canon, different discourses or Abhidhammic passages will refer to different subsets of the 22 phenomenological faculties. Thus, for instance, in the Abhidhamma there are references to the "eightfold form-faculty" which includes the first five sensory faculties plus the three physical faculties.
