Now that summer fireworks have ended and beach toys have been stored away, it's time for jukensei (受験生 entrance examination-takers) throughout the land to burn the midnight oil in earnest. High school seniors and third-year junior high students moving on to higher education — as well as elementary school sixth-graders who aspire to private junior high schools — must prepare to take rigorous late-winter entrance exams. Among other subjects, jukensei will be tested on Japanese (国語 kokugo, "national language"), including knowledge of four-kanji idioms (四字熟語, yojijukugo).

The ability to effortlessly inject more than 1,000 commonly used yojijukugo into spoken and written communication is one of the marks of a well-educated Japanese. With origins lying in classical Chinese literature, Buddhist philosophy and Japanese history, yojijukugo succinctly and elegantly describe various aspects of the human condition. They can be intimidating to foreign learners of Japanese, but a surprising number of yojijukugo have relatively transparent meanings. Today, let's nail 20 of the ones most commonly appearing on junior high school entrance exams — all are comprised of elementary school level kanji.

弱肉強食 (jyaku niku kyō shoku, weak/meat/strong/eat) means "survival of the fittest" (e.g., the weak become meat for the strong who eat them) and 異口同音 (i ku dō on, different/mouths/one/sound) is "united with one voice."