I am reading some literature on Shakespeare, and the critic has referred to marriage as a concordia discors, "a discordant harmony". In a footnote, she states:
I use "concordia discors" throughout rather than the familiar "discordia concors" because (...) Dr. Johnson distinguished sharply between the two, "differentiat[ing] the forcible yoking together of the totally diverse (discordia concors) from the harmonious combination of the true opposites, the male and female (concordia discors)".
Wikipedia has an entry for discordia concors that states:
discordia concors is a rhetorical device in which opposites are juxtaposed so that the contrast between them is striking. Dr. Johnson in his Lives of the Poets (1779) defined discordia concors as "a combination of dissimilar images, or discovery of occult resemblances in things apparently unlike. (...) The most heterogeneous ideas are yoked by violence together."
My question has to do with the metaphysics that allow us to call the harmony between male and female, the harmony between "true opposites". Can someone help me understand the distinction Johnson sees between these two words that mean, as far as I can tell "unity through diversity"?