Śivasaṃhitā 1.59

The radical uniqueness of Spirit deduced by elimination: if there is nothing else, it can only be One. This Advaita argument does not start from faith but from reasoning: multiplicity requires that the many be real; but if everything that appears multiple is, ultimately, a manifestation of the One, then multiplicity is apparent and unity is the only reality.

Tadanyo nāstīha (there exists here nothing different from It) is the Vedāntic formula of the Absolute’s exclusivity. Eko’sti sarvadā (it is always One) adds the temporal dimension: unity is not a state that is reached but the permanent condition underlying all appearance of multiplicity. Acintya (inconceivable) warns that this unity transcends ordinary thought.

The assertion of the inconceivable uniqueness of Spirit refers to the famous passage of the Māṇḍūkya Upaniṣad and its analysis of the four states of consciousness. The turīya (fourth state)—pure consciousness beyond sleep, dream, and waking—is precisely that inconceivable One that the Śivasaṃhitā points to here. Deep meditation is the door toward that recognition.