Why is 空【くう】, and not 無【む】, used to define "void", "emptiness" in a buddhist context? What are their nuances?

Question

Feel free to participate to the meta-discussion on whether this type of question (relying on buddhist terms) should be allowed on JLU.

A while back, looking at a reproduction of some famous zen buddhist scrolls in a nearby Kyoto temple, I was somewhat surprised to see that the quintessential notion of "void, emptiness" is represented by '空', rather than '無', to which my eminently non-scholar mind always gave a more spiritual overtone (beyond its everyday prosaic use).

A typical example would be the common sentence:

色即是空【しきそくぜくう】→ "form is emptiness, matter is void"

Can anybody better versed in Japanese and/or buddhist terms explain to me the nuances in meaning between these two kanji/words in a religious context?

Are there other cases where "void, emptiness" would be translated with '無' in a buddhist context?

Edit: to give a famous example of why '無' would seem a good candidate for the same concept, Yasujiro Ozu's grave in Kamakura famously bears nothing but the kanji '無', ostensibly standing for the buddhist concept of 'nothingness'.

Answer 1

I have a feeling someone smarter than me will provide an answer with better references, but I still hope this answer helps.

Not long ago I was out on a walking tour of Aoyama Cemetery and the exact same question came up. The tour guide, who has studied religion and history offered this explanation:

無　（usually な・い, but the on-yomi ム is used in this Buddhist context) means a complete absence of anything, which I think in English we would equate with void, so it would seem like the right choice.

空　（usually から, but the on-yomi クウ is used in this Buddhist context） means an emptiness as well, however, and was used to refer to the air from back before the more modern and scientific concept that the air is not in fact empty but contains molecules.

The difference between them is that the emptiness referred to by 空 is, as our guide explained, like the emptiness inside a cup. It is empty, but is conceptually bounded by the cup so that it is a space that could hold something, such as a drink.

無い on the other hand means a complete absence, without even any implication of potential. In other words, no cup.

In the Buddhist use, then, when you see it on the top layer of the five elements, (地,水、火、風、空, earth, water, fire, air, void), implies an emptiness that has a potential to contain something.

Of course, it gets a little tricky because there is no "cup" for the concept of all of existence. The void being referred to by 空 doesn't imply that anything particular should occupy that space. There is no automatic equivalent for the universe to hold like a drink would seem to be the natural thing to fill a cup. Just that the void is a vessel into which existence can happen. And from here the philosophical discussion takes over from the linguistic one.

Side note: 風 （usually かぜ, but the on-omi フウ is used in this Buddhist context）, or wind, in this context actually means "air", as back in the day, the "air" was only experienced when you could feel the wind. Before I had this discussion on the tour, I always thought they were simply differentiating wind from air.

Answer 2

無 is taken directly from the Chinese, and is often translated as "nothing." It is fundamentally a Daoist concept. You can find it prominently in the Dao De Jing and the Zhuangzi. It has many implications, from metaphysics (the opposition of being 有) to linguistics (the inability of language to capture all meaning) to the pragmatics of living life (a room is useful because it's empty) to the paradox of acting without intention (wu wei 無為). Zen (Chan) Buddhists in China borrowed this concept to help understand related ideas in Buddhism (specifically the limitations of language to capture meaning and the lack of substantial being in the cosmos). So Mu in Japanese has fundamentally this meaning--there is no substantiality to things, and language does not capture all possible descriptions of reality.

空 is also taken directly from the Chinese and (in a Buddhist context) is a technical term, a translation of the Sanskrit (Sunyata). It is often translated into English as "empty," and refers specifically to the belief in Buddhism that there is no substantial, persisting, permanent part of anything: 一切皆空. It is closely related to the concept of anatman which is rendered in Chinese as 無我. So you can see that 空 and 無 are conceptually related.

To answer the question: why is 空 used to represent the Buddhist concept of emptiness instead of 無, the answer is that 空 was selected very early in the tradition as a translation for sunyata, perhaps to distinguish from Daoist 無. The early translator could just have easily chosen 無 or even 虛. The choice has nothing to do with the basic meanings of the terms 空 and 無 and everything to do with a translator's difficult (and probably ultimately arbitrary) choice early in the tradition. 空 at the time the translator chose it, probably around the first century CE, was not a technical philosophical term in Chinese (meaning simply empty) and so would have been a good choice to translate a foreign term for its lack of conceptual baggage. 虛 and especially 無 would have been more conceptually laden, and so potentially confusing to the beginning student of Buddhism.

Answer 3

Essentially both Kanji means emptiness. But in this context Because it represents, symbolises that the emptiness is just like the vastness of the infinite sky, ether, universe that's unchanging reality, totally beyond the reach of ordinary perception. 空 means both sky, emptiness depending on context. That's the beauty of Kanji it conveys two significant meanings both relevant to each other. Also incidentally 空 is also last character in name of Sun Wukong 孫悟空 since he was bestowed his name, the great sage equaling the heavens, later achieved enlightenment after accompanying Xuanzang in Journey to the west.

As for imprinted on grave, it signifies souls are not material as dead upon death, in grave, but eternal.