At a glance
～てこそ stresses that a condition is needed to reach a good or valuable result. It is often translated as "only when", "only by", or "it is precisely by ... that".
[Verb て-form] + こそ、[good result]
努力してこそ、成功できる。 Only by working hard can you succeed.
How to form it
| Attaches to | Form | Example |
|---|---|---|
| Verb | て-form + こそ | 努力する → 努力してこそ |
| Noun | Noun + であってこそ | 健康 → 健康であってこそ |
| な-adjective | stem + であってこそ | 元気 → 元気であってこそ |
Register: somewhat formal. It is common in writing and speeches, and it is also heard in conversation. Politeness comes from the end of the sentence (できる / できます).