Into this wilde Abyss,
The Womb of nature and perhaps her Grave,
Of neither Sea, nor Shore, nor Air, nor Fire,
But all these in their pregnant causes mixt
Confus’dly, and which thus must ever fight,
Unless th’ Almighty Maker them ordain
His dark materials to create more Worlds,
Into this wilde Abyss the warie fiend
Stood on the brink of Hell and look’d a while,
Pondering his Voyage; for no narrow frith
He had to cross.
— From Paradise Lost by John Milton
The Four Elements of Empedocles is one of the earliest ontologies. While not of special interest in itself (except of course to alchemy), other double duals are comparable to it, such as the The Here and the Now and Heidegger’s Fourfold. Additionally, it is interesting to remember that it was thought that the four elements were the primitives of which everything is composed; for example bone was fire, air, water, and earth blended in a certain proportion. I am unsure of the origin of the choice of the elements: why these four and not others?
Also, note that with respect to light transmission, the four elements can be arranged in the sequence of bright, light, dim, and dark. This is not to say that fire is “good” and earth “bad”, or that fire and earth are the most different from each other. Perhaps this distinction will have some meaning later.