Forgive me for not getting this out the next day; things got a bit 'hairy' here in Tucson on January 8th.
This is a fairly short section, but we mustn’t take that as indicative of the importance of this subject! The teaching on ‘emptiness’ is arguably the most important among the teachings of the Buddha. Chapple draws the similarities with Patanjali well, though other scholars argue that Patanjali’s use of “empty” is not the same as the Buddha’s meaning.
That aside, I think it important to keep in mind that the word most often used by the Buddha in the Pali Canon is “empty,” and that in time we find the use of the word “emptiness” growing in importance. However, when a word goes from adjective to noun, we can all too easily fall into the error of reification, and indeed this has happened repeatedly in the history of Buddhism.
So, here I’ll take a page from Thich Nhat Hanh. In his commentary on the Heart Sutra, which Chapple quotes in this section, Thay says we should not take the bodhisattva Avolokiteshvara at his word without asking first, “Empty of what?” All phenomena are empty of self-nature is the response. That is, no phenomena exists from it’s own side, independent, autonomous, persistent, unchanging. There is no ‘essence’ behind, above or below phenomena. However, many Mahayana and Vajrayana Buddhists have reified this description of phenomena as empty into the ‘emptiness’ of phenomena being their essence. So it is important to remember that not only form is empty, but also emptiness is empty!
As Chapple points out toward the end of this section, ultimately there is a major distinction between Patanjali and the Buddha, despite all their similarities. Chapple says Patanjali suggests that the realization of the empty nature of phenomena delivers one to a higher state of awareness, which the Buddha denies. I think this is both unclear and perhaps not fully accurate. The Buddha of the Pali Canon, at least seems to posit some kind of awareness that is present in the state of nibbana, but the Buddha strongly asserts that even nibbana is empty of ‘self.’ That is, while all phenomena are seen as impermanent, unsatisfactory and not-self, nibanna is permanent and ultimate satisfaction, but remains ‘not-self.’ The state of liberation for Patanjali, kaivalya is said to be that which occurs when Purusha realizes its ‘self-nature.’
And though this is a small quibble, I do want to make clear that the Buddha did not proclaim that suffering results from desire. The word he used, tanha, meaning ‘thirst’ is more accurately understood to refer to the more urgent grasping and clinging to objects of desire than desire itself. In fact, the Buddha said desire for liberation was necessary for anyone to even consider yoga practice!