The word 共同 is formed by combining two independent characters, each contributing a core idea to create a new, composite meaning. The first character, 共, carries the fundamental sense of "sharing" or "together". The second character, 同, means "same" or "identical". Their fusion is not merely additive but conceptual, merging the notions of collectivity and uniformity. Thus, the formation logically progresses from "sharing" + "sameness" to arrive at the integrated concept of "common", "joint", or "mutual", where actions or qualities are held identically by a group.