Haidt's context:
In Chinese philosophy yin and yang refer to any pair of contrasting or seemingly opposed forces that are in fact complementary and interdependent. Night and day are not enemies, nor are hot and cold, summer and winter, male and female. We need both, often in a shifting or alternating balance. John Stuart Mill said that liberals and conservatives are like this: “A party of order or stability, and a party of progress or reform, are both necessary elements of a healthy state of political life.”
According to Haidt, the Mill quote continues: "Each of these modes of thinking derives its utility from the deficiencies of the other; but it is in a great measure the opposition of the other that keeps each within the limits of reason and sanity.”
