N2 — outside your level filter
こそ
こそkosoN2neutral
N and no other — picks its noun out above everything else
努力こそが人を変えるのだと思います。
doryoku koso ga hito o kaeru no da to omoimasu.
It's effort, more than anything, that changes a person. neutral
今度こそ絶対に合格してみせる。
kondo koso zettai ni goukaku shite miseru.
This time for sure, I'm going to pass. casual
All examples6
N and no other — the one noun the claim is staked on
努力こそが人を変えるのだと思います。
doryoku koso ga hito o kaeru no da to omoimasu.
It's effort, more than anything, that changes a person. neutral
困っているときこそ、周りに声をかけたほうがいいよ。
komatte iru toki koso, mawari ni koe o kaketa hou ga ii yo.
It's exactly when you're stuck that you should say something to the people around you. casual
こちらこそ、今後ともよろしくお願い申し上げます。
kochira koso, kongo tomo yoroshiku onegai moushiagemasu.
The pleasure is mine — I look forward to working with you. formal
今こそ、みんなで力を合わせるときです。
ima koso, minna de chikara o awaseru toki desu.
Now, if ever, is the time for us all to pull together. neutral
this time for sure — after failed tries, resolve put on 今度 or 次
今度こそ絶対に合格してみせる。
kondo koso zettai ni goukaku shite miseru.
This time for sure, I'm going to pass. casual
次こそは負けません。
tsugi koso wa makemasen.
Next time I won't lose. neutral
How it's formed2
All forms1
こそがkosogaalternant
が comes back after こそ when the noun is the subject (努力こそが人を変える), and は can too (次こそは). Bare こそ says the same and is commoner in speech.