Huayan thought portrays causality as an infinitely multidirectional web rather than a simple line from cause to effect. Every phenomenon is simultaneously a cause and an effect for every other phenomenon, so that no event can be isolated as a single, independent source. Cause and effect are not strictly separated in time; what appears as a cause from one vantage point may be seen as an effect from another, all within a single seamless field of reality. This vision radicalizes the more familiar teaching of dependent origination by insisting that each event arises in dependence on the totality of conditions, not merely on a local chain of factors.

The image of Indra’s Net is used to give this vision a concrete form. At each node of the net there is a jewel, and each jewel reflects all the others, while at the same time its own reflection appears within every other jewel. In this metaphor, each phenomenon both contains and expresses the influence of the entire universe, and at the same time exerts its own conditioning power on that universe. Causality thus appears as a play of mutual reflection and mutual conditioning, where nothing stands alone and nothing can be said to act or be acted upon in isolation.

Huayan further articulates this through the teaching of the four dharmadhātus: phenomena, principle, the non-obstruction between principle and phenomena, and the non-obstruction between phenomena and phenomena. Within this framework, “non-obstruction” means that things do not block or exclude one another; instead, they interpenetrate. The doctrine of “shi shi wu’ai,” the non-obstruction among phenomena, describes a world in which each event directly “enters into” every other, so that causal relations are not merely sequential but thoroughly interwoven. Causality here is the dynamic expression of a reality in which every part both depends on and determines every other part, like jewels in the net endlessly mirroring one another.