SATI or sachch, Punjabi form of the Sanskrit satya or sat, lit. truth, in the philosophical sense is essential and ultimate reality as against inessential or partial truth. Rooted in Sanskrit as meaning "to be, live, exist, be present, to abide, dwell, stay", satya means " true, real, pure," as also the "quality of being abidingly true, real, existent." Satya or satyam is a widely used term in the philosophical thought of India. It signifies eternality, continuity and unicity. In the Upaniṣads sat (truth) is the first of the three essential characteristics of Brahman, the other two being chit (intelligence) and anand (bliss). In Vedānta philosophy, the one permanent reality, Brahman, is called Sat, while the phenomenal fluxional world is named asat (non-real). In the Sikh scripture and other religious literature, sati, or sachch appears with two closely related yet distinguishably different connotations. At the metaphysical level, sati is the Ultimate Reality, truly existent, changeless and everlasting. At the level of physical existence, sati or sachch carries an ethical import as correctness, truthfulness and goodness as against kūṛ, wrongness or falsehood. The varied and wide use of the cognates of sat or sati such as satsaṅgat, satigur, satpurakh, sachkhaṇḍ, sachiār and sachchā pātsāh illustrate the role of the term in the spiritual as well as in the ethical context.

        In the Mūl Mantra,The One is also named sati besides being given other attributive names such as kartā purakh (the creative male principle), nirbhau (without fear), nirvair (without rancour), akāl mūrati (the timeless form), ajūnī (unborn) and saibhaṅg (self-existent). Gurū Arjan amplifies, "The tongue utters (mostly) your attributive names; Your primordial name is sati " (GG,1083) ; and this "True Name of God is ever solace-giver" (GG, 284). Elsewhere in the Holy Scripture sachu sabadu (the Word Truth) and sachā sabadu (the True Word) or simply sach(ch)ā (the True One) have been used as synonyms of satinām to describe God (GG, 34, 580, and 581). Besides using sati or sachch as a name for God the words have also been used as adjectives for the Ultimate Reality which is immutably true, transcending time and space, beyond life and death, never old, forever new. In the opening line of, Japu, he is described as ādi sachu, jugādi sachu; hai bhi sachu, nānak hosī bhī sachu--- True (was He) in the (beginningless) beginning, in the beginning of the cosmic time; True is (He in the present) too, True shall (He) be, O Nānak, (for ever in the future) (GG,1). Towards the end of Japu, the highest spiritual region, the abode of the Formless One, is described as sach khaṇḍ.

         According to Sikh cosmogony, the universe was created by the Transcendent God out of Himself at His own pleasure, and in His own will. He may withdraw it into Himself when He so wills it. The created world has therefore a dual nature. It is sat (real and no illusion) because it was created by the Real One, who is immanent in it while He wills it to last : āpi sati kīā sabhu sati (He Himself is Truth and true is His creation) (GG, 284). At the same time it is not sati (immutable and ever-existent) because its existence is contingent upon His Will. Thus, although the universe of time and space emanates from sati (the Ultimate Reality), it does not exhaust the latter nor limit it within its own temporal and spatial limits. The Transcendent sati is alakh (unknowable) and cannot be known because the created cannot know the creator (karte kī miti na jānai kīā) (GG, 285); yet the agam (unapproachable) and the agochar (inaccessible through the senses) can be comprehended through the Gurū's sabad (instruction) (GG, 130). This is accomplished in two ways. One, the Gurū by opening the inner eyes of the seeker's higher consciousness reveals to him the Satya that permeates the entire creation, so that "Nānak’s Master, who is beyond the world and beyond the revelations of scriptures, becomes distinctly manifest" (GG, 397). Secondly, the seeker who through meditation upon the sati internalized it himself becomes one with sati (GG, 284). In Sikh theology this happens with God's grace. In fact, sati (God) in grace reveals itself to the chosen one through the Gurū, who is already so chosen and becomes one with sati. The medium of communication in this process is sabad (word) or bāṇī (Gurū's utterance). "The Gurū, the bāṇī and Brahm are all the same and are realized through the sabad (GG,39). God's nadar (grace) is sovereign, subject alone to His razā (will). However, two circumstances can help the seeker to deserve and receive it. One is meeting with the satigurū (True Gurū) (GG, 33, 313), and the other is to know the jugati (method), which comprises "cleansing the mind of the dirt of kūṛ (falsehood) and cultivating love of sachch" (GG, 468).

        This brings us to the existential level, where sati or sachch is an ethical category which sustains dharma, the governing principle of the world of time and space. It forms the basis of hukam (law), niāu (justice) and chaṅgiāī (goodness). At the individual level, sachch as truthfulness is the most desirable virtue. "Sachch (truth) is supreme, yet sachu achār (true living) ranks above it" (GG, 62).

        Sikhism is a humanitarian creed, in which theological is closely related to the sociological aspect. Sati (truth) is here not only an abstract notion of Supreme Reality, but is also a practical principle of human conduct. The ideal set for a Sikh is to become sachiār (truth-seeking person), and the basic human problem, set forth in the opening stanza of Gurū Nānak’s Japu, is "How to become sachiār? How to demolish the wall of kūṛ (falsehood)?" And the solution suggested in the line immediately succeeding is "to conduct oneself under His hukam (Will) and razā (pleasure)" (GG,1). In practical terms, Gurū Nānak instructs, "Test your mind against the touchstone of truth : guided by Gurū's light, deal in the merchandise of truth ; be a gurmukhi (gurū loving) so that you despise kūṛ and are in love with sach: loving sach, you shall be absorbed in sach and shall find the jewel of nām (satinām) which lies (dormant) in your own mind" (GG, 22). Gurū Amar Dās declares, "Honour and good name arise out of true word; seeing sachu and speaking sachu, body and mind acquire truth" (GG, 69).

        That truthful living implies truthful actions (sachu karam, or sāchī kār) and true discipline (sachu sañjam) at individual level is obvious, but Sikhism being a congregation based faith the Gurūs also emphasize need for true company (sachī saṅgat or satsaṅgat)(GG, 69, 586). Satsaṅgat is defined as "a school for learning virtue" (GG, 1316) and "a place where the One (God's) Name is solely talked" (GG, 72).

        Sati or sachch is both the name given the Supreme Reality and the supreme good to be realized spiritually as well as in individual and social life. This many-splendoured truth is "the overlord of all, accessible only to one whom He blesses" (GG, 922). It is "the panacea for all ailments; it flushes out the filth of sin" (GG, 468).