What it means
こそ emphasizes the word or phrase immediately before it, presenting that element as especially important, definite, or exemplary. It can express contrast, as in “X in particular” or “X, rather than something else.” In てこそ, it often means that a result is possible only through the stated action. In からこそ, it emphasizes the reason, meaning “precisely because.” The sentence ending can be familiar or polite without changing the meaning of こそ.
Usage note
こそ is a focus particle, so it does not itself make a sentence polite. Do not confuse こそ with しか, which means “only” and normally requires a negative predicate. When the meaning is “precisely because,” include から explicitly, as in だからこそ.
How to use it
田中さんこそ、今回の代表にふさわしいです。
Tanaka is precisely the right representative for this occasion.
今だからこそ、家族と過ごす時間を大切にしたいです。
Precisely because it is now, I want to cherish the time I spend with my family.
実際に使ってこそ、その道具の価値が分かります。
Only by actually using the tool can you understand its value.
田中さんこそ、今回の代表にふさわしい。
Tanaka is precisely the right representative for this occasion.
今だからこそ、家族と過ごす時間を大切にしたい。
Precisely because it is now, I want to cherish the time I spend with my family.
実際に使ってこそ、その道具の価値が分かる。
Only by actually using the tool can you understand its value.
Example sentences
私は雨の日だからこそ、図書館で落ち着いて勉強できます。
It is precisely because it is a rainy day that I can study calmly at the library.
毎日の小さな努力こそ、試験に合格するための一番確かな道です。
Daily small efforts in particular are the most reliable path to passing the exam.
困