The 25 Sloka compacting of the MahaPrajñāpāramithā is the Hridaya Sūtra [‘Heart Sūtra’]. It is to be read and interpreted only as supplement to the Vajrachedika for its very tight phrasing can seriously miscue the entrant.
If the Diamond Sutra is loopy, circuitous, the Heart Sutra, is in-your-face direct. Numerous European language translations from Max Muller to Edward Conze going back over a century are available on the Web.
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!‘. In contemporary language: The [Self-Scuttling] Sight-Insight on the very nature of Sight-Insight. In other words, Shūnyam.
The Sūtra approaches this axial verse by introducing a celebrated line: ‘Form is not different from Emptiness; Emptiness, from Form‘. And to do this it introduces two words: Shūnyathā and Nāmarūpam translated into English as Emptiness and Form.
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’.
If it had any other purpose it was to differentiate the philosophical substance of ‘That’ from its routine grammatical chores. Or limit the risk of ‘That’ being taken as an entity. These would have been entirely legitimate. [ Immanuel Kant: ‘The Principles Of Knowing‘]
But it was rarely used in this service and very soon after its construction [and predictably so], ‘That-ness’ took on a philosophical life of its own. You can see this as much in the early Vedanthic literature as in the later Buddhist texts.
What happened with Tát: Táthātā is exactly what happened much later in the construction of the distinction: Shūnyam: Shūnyathā.
Shūnyam is to ‘That’ as Shūnyathā is to ‘That-ness’.
But the derivative extension of Shūnyathā continued to firmly retain the original Logical Form of its parent even if never effected. 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 a muddled ‘Whole’.
As Nagarjuna, the Buddhist Scholar-Monk put it: ‘He who is in harmony with Emptiness [Shūnyathā] is in harmony with all things. Beyond good and evil, profound and liberating, [it] has not been tasted by those who fear what is entirely groundless.’
The Diamond Sūtra would laud the encouragement but stop-short of making the same claim [For ‘No Achievement’ is the achievement]. And Shūnyam would concur.
The traditional Madhyamaka interpretation limits itself to to the Principle of Co-Dependence to arrive at Shūnyathā. Instead its proper unfolding requires a comprehensive application of the Self-Negating Expression in the ‘Backward Step’. All differences between them are reducible to this event. [See the Posts]
I sat in once on a lecture by a celebrated Tibetan monk who went on about the ‘Stages of Emptiness’. There are no ‘stages’ to Emptiness. If there were, it wouldn’t be Emptiness.
To hold forth, as I have seen, about the emptiness of tables and trees in a literal take on their supposed hollowness is to entirely miss the point. The table and tree may be hollow or full. It is the observer not the observed that is ‘Empty’.