Yin Yang are a couplet which can seem to be the equivalents of the binary 1, 0 which lie at the heart of all computer logic. But there is a crucial difference, the emphasis in Yin Yang is on their complementary relationship. For example, if Yin is night and Yang is day then we would not know either without the other. In every situation where there is change, we can define it in terms of Yin Yang. For example, when we move an arm up and out (Yang), it is balanced by another part of the body sinking down (Yin). Our attention is usually captured by the Yang movement which could be described as the opening aspect of it. It is crucial in Qigong to recognise that any Yang movement has a root in its closing Yin aspect.