The word that expresses Īśvara is the syllable oṃ.

From Definition to Practice

Sūtra 1.27 moves from the philosophical definition of Īśvara established across 1.24–1.26 to a concrete practical instruction: tasya, of that Īśvara, vācakaḥ, the expressive word or verbal designation, praṇavaḥ, is the syllable oṃ. This is a significant transition within the text's structure, since the immediately following sūtra, 1.28, will instruct the practitioner to repeat praṇava and contemplate its meaning, converting the preceding several sūtras' philosophical argument into an actual technique of practice available to any aspirant regardless of temperament.

Vyāsa on the Relationship of Word and Referent

Vyāsa explains vācaka here as designating a relationship stronger than arbitrary convention: the syllable oṃ is held to be eternally and naturally, not merely conventionally, connected to Īśvara, comparable to how the relationship between a father and son is a natural one rather than an assigned label. This claim draws on a broader current in Indian linguistic philosophy, associated with schools that treat the relationship between certain words and their meanings as inherent rather than arbitrary, in contrast to other schools that treat all word-meaning relationships as conventional.

Praṇava's Place in the Broader Text

Vācaspati Miśra notes that praṇava's significance here echoes its prominent role in Vedic and Upaniṣadic literature, where oṃ is treated as the primordial sound or symbol underlying all speech and, in some traditions, all of manifest reality, though Patañjali's own usage remains specifically tied to Īśvara as defined in the preceding sūtras rather than to the fuller cosmological claims found elsewhere. Vijñānabhikṣu reads the choice of praṇava as practically significant because sound, unlike visual imagery, can be repeated continuously and silently, making it especially suited to sustained meditative repetition (japa) of the kind prescribed in 1.28. Hariharānanda Āraṇya connects this sūtra forward to 1.29, which promises that from this practice come both pratyak-cetanā-adhigama, the turning of awareness inward toward one's true nature, and the removal of obstacles (antarāya) catalogued in 1.30, situating praṇava practice as a specific, complete technique within the broader arc of Book One's argument, moving from definition through practice toward outcome across these several connected sūtras.

A Practicable Technique From Abstract Definition

Sūtra 1.27 supplies something concrete after several sūtras of careful definition: an actual syllable to work with, connecting the philosophy of 1.23–1.26 directly to practice.

Repetition as the Immediate Application

Vijñānabhikṣu's observation that sound suits sustained repetition points directly to the technique specified in 1.28, japa, repeated recitation, paired with reflection on meaning, rather than oṃ functioning as an isolated symbol to simply contemplate visually.

A Simple Practical Approach

1. Repeat the syllable oṃ quietly or silently, at a steady, unhurried pace, without straining the voice or breath.
2. Allow attention to settle on the sound itself before adding reflection on its associated meaning.
3. Bring to mind, gently, the qualities defined in 1.24–1.25: freedom from affliction, unsurpassed knowledge.
4. Notice whether this practice supports steadier, calmer awareness compared to sessions without it.
5. Treat this as one available technique among the several already outlined in 1.20–1.23, not a replacement for all others.

Read together with 1.28's explicit instruction to repeat and reflect, 1.27 completes the movement from Patañjali's careful philosophical definition to an ordinary, repeatable practice open to any sincere practitioner.

A frequent misreading treats oṃ here as simply one sacred sound among many interchangeable options, missing Vyāsa's specific claim that the relationship between praṇava and Īśvara is a natural, not merely conventional, one, comparable to a father-son relationship rather than an arbitrary linguistic label assignable to anything. A second misunderstanding imports the full cosmological weight oṃ carries in certain Upaniṣadic contexts, where it represents the totality of manifest reality, without noting that Patañjali's own usage here remains specifically tied to Īśvara as carefully defined in 1.24–1.26, a narrower and more precise claim than a general cosmological pronouncement. A third error treats this sūtra as complete in itself, missing that its practical significance depends on 1.28's explicit instruction to repeat the syllable and reflect on its meaning; without that following sūtra, 1.27 would remain a definitional claim rather than a technique. Some modern presentations also assume the historical or comparative-linguistic debate about word-meaning relationships is settled in Vyāsa's favor, when this remains a contested position within classical Indian philosophy of language rather than an uncontroversial premise shared by every school. Reading 1.27 as a hinge connecting philosophical definition to the practical technique specified next in 1.28 keeps both its precision and its practical intent clearly in view.