  All other causal factors are either ‘non-substrate’ causes or ‘instrumental’ causes. A non-substrate cause is one which inheres in the substrate cause. Thus, though not being the substrate, it is closely connected with it. The conjunction of threads is said to be a non-substrate cause of a piece of cloth. Another example is often cited. The non-substrate cause of the colour of a piece of cloth is the colour of the threads (which colour inheres in the threads, in which inheres the effect, the colour of the cloth). Any other causal factor is called an instrumental cause, for example, the weaver’s shuttle or the weaver herself. Why did the Naiyāyikas distinguish between non-substrate causes and the remainder? Perhaps it was an attempt to differentiate between those causes which must continue to exist for the effect to exist, and those which need not. If the threads were to lose their colour, then the cloth would lose its, and if the threads were to become disjoint, the cloth would cease to exist altogether. If, however, the weaver dies, having already woven the cloth, or if the shuttle is subsequently destroyed, it will not affect the continued existence of the effect.