The author argues in this paper that consciousness may never be defined or explained with entities and properties, neither with brains and neurons, nor with particles, waves, and fields. Instead, a system is proposed in this paper, with matter, energy and lives as its components, and with all its components defined as changes. Based on the systematic relationships among those components, the author’s definitions or explanations of consciousness are: • Ontologically, consciousness is universal, since it may only be the systematic (...) distinction between matter and energy. • Epistemologically, consciousness is unique, since it may only be the energy that is formalized, qualified or diversified systematically by the matter. • Semantically, consciousness is a meaningless language with lives as its only meanings. In other words, only lives are, but consciousness is not, the causality of mental activities. Such defined or explained consciousness might be useful for us to find a more unified framework for neuroscience, psychology, the philosophy of mind, and the studies of artificial intelligence. (shrink)