I first came across this one on Twitter. The language is just too modern and the ideas expressed too neatly and philosophically for this to be from the Pali Canon. It doesn’t sound, in tone, like anything I’ve read in the Mahayana scriptures either.
It’s in fact from a book called The Teachings Of Buddha, by Bukkyo Dendo Kyonkai, a Japanese organization. In a fuller version it’s:
As has been pointed out, all things appear and disappear because of causes and conditions. Nothing ever exists entirely alone; everything is in relation to everything else. Wherever there is light, there is shadow; wherever there is length, there is shortness; wherever there is white, there is black. Just like these, as the self-nature of things cannot exist alone, they are called non-substantial.
The Teachings of Buddha may contain scriptural material, but this passage seems to be from a section that is “about Buddhism” rather than representing a primary source. The Buddha really didn’t talk in terms of everything existing in relation to everything else.