On Being Relative and Absolute in Relativity

In teaching relativity, what is stressed is its being relative while what is ignored is its being absolute. Examples of the absoluteness include the principle of invariance for velocity of light, the principle of special relativity, the principle of general relativity, eigenlength, eigentime, Minkowski four dimensional space-time. It must be pointed out that the relative and the absolute are the two aspects of the law of the unity of opposites, and only by rightly comprehending their relations, can the nature of relativity as well as the law of nature be better understood.