～こそ
precisely / exactly
～こそ attaches to a word to single it out emphatically as the very one: “precisely X”, “X is exactly the one”. It usually replaces は or が, upgrading a plain topic into a spotlighted one.
Whereas ～さえ picks an extreme example to imply “even X (let alone the rest)”, こそ picks the right one out of the candidates: not the others — this one. You also hear it in the set phrase こちらこそ (“the pleasure is mine”).
1. Emphatic singling out
Use こそ to insist that the marked word, and not anything else, is the one that counts. It is common in resolutions like 今年こそ (“this year for sure”).
今年こそ日本に行きたい。
“This year for sure, I want to go to Japan.”
- 今年（ことし）= this year
- こそ = precisely / for sure
- 日本（にほん）= Japan
- に = destination marker
- 行きたい（いきたい）= want to go
2. ～からこそ: precisely because
Attached to から (“because”), こそ stresses that this reason and no other is what justifies the conclusion. It often introduces a reason the listener might not expect.
今だからこそ、新しいことに挑戦するべきだ。
“Now is exactly the time to try something new.”
- 今（いま）= now
- だから = because it is
- こそ = precisely
- 新しい（あたらしい）= new
- こと = thing
- に = target marker
- 挑戦する（ちょうせんする）= to take on a challenge
- べきだ = should
How to form it
Noun + こそ (replacing は/が); ～から + こそ for emphasized reasons
- 今年（ことし）= this year → 今年こそ（ことしこそ）= this year for sure
- これ = this → これこそ = this is exactly (the one)
- 頑張ったから（がんばったから）= because (I) worked hard → 頑張ったからこそ（がんばったからこそ）= precisely because (I) worked hard
Key idea
こそ shines a spotlight: out of all the possibilities, the marked word is the very one. Read X こそ as “X is exactly the one that ...”.
Other N3 grammar
Updated .