只有…才【zhǐyǒu … cái】

只有…才 says the result depends on one condition: without it, no result. 只有 opens the condition, and 才 goes before the verb of the result, after its subject.

The result half usually has a modal verb after 才 – 能, 会, 可以 – because it describes something that can happen once the condition is met.

才 goes after the subject

• × 只有周末，才我有时间 → 只有周末，我才有时间

才, not 就

只有 always pairs with 才. 只要…就 is the opposite case – the condition is enough, but there may be other ways. Put side by side:

• × 只有你去，他就会去 → 只有你去，他才会去
• × 只有多练习，能说好中文 → 只有多练习，才能说好中文