If the Diamond Sutra is loopy, circuitous, the Heart Sutra, is in-your-face direct. Necessarily so given its purpose of radical condensation. And its boldness, written as it was 2,500 odd years past, when religion and ritual enforced all social creed, can be breathtaking.
The pivotal line from the Heart Sūtra which the Nalanda Translation Committee wisely decided to leave in the original Sanskrit [and I, less wisely, have chosen to translate] is the following:
‘The Prajñā-Pāramithā Mantra is said in this way: Om Gatheh! Gatheh! ParaGatheh! ParasamGatheh! Bodhi Svaha!’ [‘My understanding, released, soars, takes flight. Svaha!‘.]
This seemingly cryptic verse can be rewritten in more prosaic phrase as follows: The denouement that yields the self-scuttling sight-insight [‘Observation-Understanding’] on the very nature of sight-insight. In other words, Shūnyam.
This axial verse is approached with, made more meaningful, in the approach line: ‘Form is not different from Emptiness; Emptiness, from Form‘. A cryptic summary that I have seen routinely get grossly disfigured by half-done Gurus.
Few texts comes closer to the truth of Shūnyam than the Heart Sūtra. Where is the slip?
Shūnyam is the formal Sanskrit for Śūnya in common-speak. Etymologically, Shūnyam originate in the notion of hollowness, of ‘Empty Inside’.
The term ‘Empty’ or ‘Null’ as used in English translations of Shūnyam originate directly from the vocabulary of Classical Logic as does the word ‘Form’ as used in the Heart Sutra. [Although no guru, fee-speaker or book-writer I have met is aware of this root, which might explain their wildly creative interpretations of these two terms.]
Shūnyam itself is not to be confounded with the numerous versions of Śūnya with a suffix that evolved in the regional Dharmic literatures well into the 10th Century [ŚūnyaBrahman, ŚūnyaPurusha et al]. Or the selective use of the term ‘Emptiness’ in others [Kashmiri Shaivism, the Southern Bhairava et al]
As with Shūnya, there are a variety of definitions of Shūnyathā to pick from beginning with the Theravada and reaching into all variants of the Mahayana.
The later derivative construct of Shūnyathā found its inspiration in an established earlier divide: Táthātā and Tát.
What’s the difference? Táthātā, typically translated into English as ‘That-ness’ [also as Suchness, Thusness] is the abstraction of Tát [‘That’]. The problem is that you cannot abstract ‘That’ which has already gone well beyond such distinctions as ‘Abstract and Concrete’. It can only be abstracted by one who doesn’t understand its intent.
If it had any other purpose it was to differentiate the philosophical substance of ‘That’ from its routine grammatical chores. This would have been entirely legitimate. But it was rarely used in this service and very soon after its construction [and predictably so], ‘Thatness’ took on a philosophical life of its own.
What happened with Tát: Táthātā is exactly what happened much later in the construction of the distinction: Shūnyam: Shūnyathā.
Again and as before, one does not abstract ‘True Nothing’. Shūnyam itself is the leap from the limit of abstraction. The attempt at abstraction is only done by one who does not comprehend its intent or meaning.
But the derivative extension of Shūnyathā continued to firmly retain the original Logical Form of its parent. In fact it’s most consistent definition in the higher texts has been ShūnyathāShūnyathā: ‘The Emptiness of Emptiness itself’, a full-blown Self-Eating Expression.
The result was consequential. Depending on the source, Shūnyathā has been interpreted both as a synonym for a conceptualized Shūnyam and otherwise as a mystic expression for some special capture of Awareness, Consciousness, or the Whole.
If you are interested in more detail, the later extensions, principally the Madhyamaka, pivot off the Principle Of Co-Dependence without reaching into the Axioms of Sight and ‘Self” in exact parallel to the Vedanthic stop at ‘Being: Consciousness’. [Hence the continued necessity for two-part labels for the terminus.]