〜てこそ
JLPT N2:only by / only when
Marks X as essential to the result or value that follows: only by doing X does Y become true.
How to form it
- Add こそ to the て-form: 使って becomes 使ってこそ.
- The second half states a value or result that depends on X; it is not merely the next event in time.
Examples
失敗してこそ学べることがある。
There are things you can learn only by failing.
実際に使ってこそ言葉は身につく。
Only by actually using a language do you acquire it.
Common mistakes
- Using it for a mere sequence where the first action is not essential to the result.
Similar meaning
- 〜て初めてonly after / not until
て初めて says Y first becomes possible or known after X; てこそ says X gives Y its value.