Why does 共 have an on-reading of 'kyou'? Its Chinese reading is 'gong', and the 'gong' I'm most familiar with is 公, which has an on-reading of 'kou'. Why did some 'gong's become 'kou's and others 'kyou's? Was it some evolution between Early Middle Chinese and Modern Mandarin that caused 共 and 公 to gain the same pronunciation?
And then 洪 is 'kou'? Is the 共 radical not a sound-radical? And it's 'hong' in Chinese. HELP ME OUT HERE, EAST ASIA.