noun
complete reversal of values or ways of thinking
A yojijukugo describing a dramatic shift in perspective where one now considers what was previously thought wrong to be right, and vice versa. Often used in literary or philosophical contexts.
彼の意見は昨非今是で、以前と全く逆になった。
His opinion has undergone a complete reversal; it is now the exact opposite of what it was before.
A yojijukugo composed of 昨 (yesterday, past), 非 (wrong), 今 (now), and 是 (right), literally meaning 'yesterday's wrong is today's right'. The exact historical origin is uncertain, but it reflects a classical Chinese-derived expression for a radical change in judgment.