Are in pairs. Such as the moon and the sun, dark and bright, cold and hot, passive and active, etc. But yin and yang are not static or just two separated things. The nature of yin yang lies in interchange and interplay of the two components. Yin and yang are opposite in nature, but they are part of nature, they rely on each other, and they can’t exist without each other. The balance of yin and yang is important.