I am able to show that the four phrases exemplified by “form is emptiness” were once a reference to the well-known simile, “Form is like an illusion”. As the Prajnāpāramitā corpus expanded, the simile became a metaphor, “form is illusion”. It was then deliberately altered by exchanging “illusion” for “emptiness”, leading to the familiar phrases.
This connection opens the door to reading the Heart Sutra, and the early Prajnāpāramitā sutras more generally, along the lines of Sue Hamilton’s epistemological approach to the Pāḷi suttas; i.e. as focussed on experience and particularly the meditative experience known in the Pāḷi suttas as “dwelling in emptiness.” In this view, the Heart Sutra makes sense on its own terms without having to invoke paradox or mysticism.