The characters combine literally and elegantly to mean: “To take (以) history (史) and use it as (为) a mirror (鉴).”
The concept of 以史为鉴 is a cornerstone of Chinese civilizational thought, reflecting a deep-seated belief that the past holds the key to the future. Its most famous origin is attributed to Emperor Taizong of the Tang Dynasty (唐太宗), one of China's most revered rulers. He famously said: “以铜为镜，可以正衣冠；以古为镜，可以知兴替；以人为镜，可以明得失。” (Using bronze as a mirror, one can straighten their clothes; using antiquity as a mirror, one can understand the rise and fall of states; using people as a mirror, one can clarify one's gains and losses.) This quote elevates the study of history from an academic pursuit to a practical tool for governance and self-cultivation. This value is intrinsically linked to the concept of the Dynastic Cycle, where the patterns of a dynasty's rise, prosperity, corruption, and collapse were meticulously recorded so future rulers could avoid the same pitfalls. Comparison to Western Culture: A similar Western concept is George Santayana's phrase, “Those who cannot remember the past are condemned to repeat it.” However, there's a key difference in emphasis.
This is a formal and highly respected phrase. You will almost never hear it in casual, everyday conversation between friends.
The connotation is always serious, wise, and respectable. Using it demonstrates education and a thoughtful perspective.