I return to the story of the Penumbra and the Shadow, the second to last story (followed by Zhuangzi's dream of being a butterfly) in Chapter Two of the Zhuangzi. The Penumbra asks Shadow why he is so apparently indecisive, now standing, now sitting. Shadow replies with some questions of his own. How could he know why he is as he is? Is he dependent on something else that is itself dependent on something else ad infinitum? Does he depend on something like a snake does its skin?
A penumbra is the diffused light which surrounds a shadow (umbra). It is not quite a shadow; it is literally (in Chinese) "neither-of-the-two"; it is neither shadow nor light. It is interpreted as the shadow of a shadow. There are penumbral eclipses of the moon in which it is not the earth's solid shadow that passes across it but the sun's light diffused by the close passage of that shadow. As the shadow of a shadow is there anything more dependent? And yet it deigns to ask Shadow why it appears so indecisive.
Shadow's response is not easily understood principally because he in effect declares himself to likewise be "neither-of-the-two", which is to say he answers with paradox. Is he dependent on something else? Absolutely. And is that something else likewise dependent on something else? Of course. Everything is dependent on everything else. All things are mutually interdependent. But if everything is dependent on everything else, as Guo Xiang points out in his commentary (the first extant), then nothing is truly dependent on anything. Penumbra is dependent on Shadow, but is it not also the case that Shadow depends on Penumbra? Without a penumbra there would be no shadow; causation, like mutually generating opposites, goes both ways and thereby cancels itself out. Seen mechanistically, causation is linear and uni-directional; seen from the perspective of the Whole, it is circular and ambi-directional.
Shadow is "neither-of-the-two" because he is neither dependent nor independent; he is "self-so". And this is "true" independence. Does Shadow depend on something like a snake does its skin? Absolutely. And yet the snake sheds that skin. If it truly depended on that skin, then the snake that was is not the snake that is. The snake is a dynamic, "self-so" phenomenon that is ultimately uncaused and non-dependent just as is the uncaused, world-arising where everything is accomplished though nothing is done.
Zhuangzi asks us how it would be to “depend on nothing”, and answers that that would be to wander far and unfettered. Yet this dependence on nothing is predicated on an understanding that we depend on everything. “Hand it all over to the inevitable”, entrust yourself to Mystery — releasing ourselves into the Whole we participate in the true independence (non-dependence) that is the Whole.
You can check out Scott's writings on Zhuangzi here.