Nāmarūpam has a seriously slippery feature to it: Self-Reference.
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.]
The translators of the Hridaya [‘Heart’] Sūtra had struck gold with the pick of the English words to translate Shūnyam: Shūnyathā by reaching into its vocabulary.
But they were flailing around for an equivalent choice for the term Nāmarūpam. [In fact by this time its interpretation in the Sanskrit itself had become entirely flaccid.]
Then the Translators noticed the English word ‘Form’ which happened to be part of the extended vocabulary of Classical Logic. It had a nice ring to it and the meaning appeared very close to the word Nāmarūpam.
And so they went with ‘Form’, a palliative compromise. [The word first appears in Plato’s ‘Theory of Forms’ which is probably where it was noticed. The English word ‘Idea’ originates here.]
But Nāmarūpam is not exactly ‘Form’. And the two words are not perfect translation matches. And to see where and how they are different can make all the difference.
‘Form’ as commonly used in Classical Logic is: ‘Something that is marked, has taken shape’. A line, a curve, a color, a smell, a melody, a scratch. Logic comes alive, is operative, only in the abstract, only in the world of Form.
But Nāmarūpam does not exactly overlap with the ‘Form’ as defined by the Logician. Nāmarūpam like Form, is ‘Something that is marked, has taken shape’. But Nāmarūpam, unlike the Logician’s Form, an ‘Objective’ presence, includes within its domain all ‘Subjective’ presence’ as well.
Feeling is Nāmarūpam, a mental-image is Nāmarūpam, internal-dialogue is Nāmarūpam. All that you see with your eyes closed or hear with your ears plugged are part of Nāmarūpam. If you can name it, mark it, express it, put a metaphorical finger on it, it is part of Nāmarūpam.
All references to Nāmarūpam are already contained in Nāmarūpam as are all thoughts you have in response to it. If you slip on its self-referential feature you will confound Nāmarūpam with Awareness, Consciousness, Presence, Everything and other such heavy concepts, and find yourself thrashing around on the tails of the Self-Loop.
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.
In the tradition of the Buddhist Madhayamaka, Nagarjuna’s definition of ‘Emptiness’ emerges directly from the exploration of Co-Dependence based on the ‘Sidewards Inquiry’. But it needs to complete the circle, take the ‘Backward Step’, touch the terminus at Shūnyam to properly mount on Shūnyathā.
[The material can be expanded substantially if one were to go into the later evolution of Platonic Form and the Academic Philosopher’s love of ‘Universals’. But I shall stop here.]