Red Pine has this to say on the line “form is emptiness and emptiness is form” in his translation of and commentary on The Heart Sutra:
That form is is empty was one of the Buddha’s earliest and most frequent pronouncements. But in the light of Prajnaparamita, form is not simply empty, it is so completely empty, it is emptiness itself, which turns out to be the same as form itself.
The logic of this, which has become the most famous statement in Mahayana Buddhism, goes like this: Form, or any other entity of the mind, is defined by the mind and exists only because we claim it exists. The only thing that exists, in this case, is our definition of form. Form itself is empty of anything that could be called self-existent. Whatever we use to define form, it is dependent on something else. Thus, the essential nature of form is emptiness. But emptiness is simply another name for reality–not just a part of reality, for reality has no parts, but all of reality–though neither can reality be considered to be a whole. The essential nature of reality is that it is indivisible, or empty of anything self-existent. But if form is equivalent to emptiness, or the indivisible fabric of reality, then emptiness must also be equivalent to form. Thus, Avalokiteshvara goes beyond the understanding of early Buddhists, who understood that form is empty, and surprises Shariputra with the statement ’emptiness is form.’ Avalokiteshvara turns Shariputra’s understanding of the Abhidharma upside-down and tells him that in the light of wisdom the seamless fabric of reality is equivalent to any attempt to separate reality into parts, including parts, such as form, that are attempts to account for all of reality, as we experience it. The absence of anything self-existent is the true nature of all that we experience, however distorted that experience might be by the matrix of our minds. But it is also the true nature of reality.
This, then, is the hub around which this sutra turns, the equation that puts an end to the dualistic conception of reality. The problem that arises when we reflect on our experience is that we reflect on our experience. We think, therefore we are. And once we are, we are in trouble, forever divided by what we use to define our existence. In analyzing the elements of this particular definition of self-existence, namely the Five Skandhas, Avalokiteshvara sees that they are empty of anything permanent, pure, or inherent; they are empty of anything real. They are empty as a group, and they are empty individually. They are so completely empty, we might be tempted to say that they do not exist. But we can’t say that they do not exist, because they exist as delusions. And we can’t say they do not not exist, because they are completely empty. Thus, as used by Avalokiteshvara, and by Mahayana Buddhists in general, the word ’emptiness’ does not mean nothingness. It is a double negative that stops short of establishing a positive. Emptiness means indivisibility.
Something that is empty of self-existence is inseparable from everything else, including emptiness. All separations are delusions. But if each of the skandhas is one with emptiness, and emptiness is one with each of the skandhas, then everything occupies the same indivisible space, which is emptiness, and the same indivisible time, which is also emptiness, and the same indivisible mind, which is emptiness again. Everything is empty, and empty is everything. Avalokiteshvara denies all views regarding the skandhas that would regard any of them as real by telling us that ‘form is emptiness.’ But he also denies all views that would regard any of them as annihilated by telling us that ’emptiness is form.’ Neither do the skandhas exist, nor do they not exist. What we are left with is a koan: ‘form is emptiness and emptiness is form.’
Tempting as it may be to dismiss things like this as Sophistic nonsense, I’ve found, the longer I’ve studied and practiced Buddhism, that what at first looks like the ramblings of a particularly precocious, but nonetheless stoned, teenager will yield increasingly profound insight upon increasingly careful contemplation. How can we say of something that neither does it exist, nor does it not exist? Consider space at either the gross level of cosmological objects or the fine level of sub-atomic particles.
Think first of the gross level. It’s pretty easy for most moderns to grasp that our solar system is floating, with vast expanses of space around and between the objects of which it’s composed. There is, for instance, our planet with its atmosphere (and some miscellaneous detritus at various levels of orbit) and, tens of thousands of miles away, the moon. Does the space between the edge of our atmosphere and the moon exist? Since it’s empty space, a vacuum or void, we can’t claim that it exists, but at the same time, since our atmosphere doesn’t touch the moon–something separates them–we can’t claim that it doesn’t exist either.
And zooming in through the earth’s components (its atmosphere, oceans, crust mantle, core, etc.) to the fine level, it’s not much harder to imagine sub-atomic particles floating in a similar way in that same space. In fact, at that level, there’s even less floating in even more overwhelming space. So space not only surrounds at the gross level, but it also pervades at the fine level. And at that fine level, we’re starting to find that those sub-atomic particles themselves–composed, it seems, of quarks, which are in turn composed, perhaps, of vibrating strings of energy, which are themselves composed of we may never know what–are more like space than like something solid, which suggests that space–which doesn’t quite exist or quite not exist–surrounds, pervades, and even composes our physical world.
This may still seem like precious, Sophistic nonsense, but it seems to me that there’s naught but emptiness. All else is only delusive conception.