In his commentary on the Chandogya mantra 6.2.1, “sat eva soumya idam agra aaseet ekam eva advidiiyam…” Sankaracarya explains, “The word ‘sat’ refers to Existence, subtle, without distinction, all pervasive, One, taintless, partless, Consciousness. The word ‘eva’ is used for emphasis. (Sadeva – sat iti astitvamaatram vastu nirvisesham sarvvagatam, ekam, niranjanam, niravayavam, vijnaaanam yat aagamyate sarvavedantebhyah. Ekasabdah avataaranaarthah.) ‘One only’’Without a second’ means that It (Existence) has no second thing different from Itself”.