What is the difference between shu'ab (branches) and arkan (pillars), and how is each defined?

"Shu'ab" (شُعَب) is the plural of "Shu'bah" (شُعبة), which means a faction or a piece of something. It can also refer to a pillar or a complement. As for "Arkan" (أركان), it is the plural of "Rukn" (ركن), which is the strongest side of a thing upon which it stands. A "Rukn" is an essential part of something without which it cannot exist. The difference between them is that if a "Rukn" is absent, the thing itself ceases to exist. However, if some "Shu'ab" are absent, it does not necessarily lead to the non-existence of the origin of the thing.