只有 … ，才 … (only if)

The only way in

• The building door needs a code, and only residents know it.
• only if只有zhǐ yǒuknows知道zhī dàocipher密码mì mǎ，talent才能cái néngto go in进去jìn qù。 — "Only if you know the code can you get in."

only if只有zhǐ yǒu A，only then才cái B

• only if只有zhǐ yǒu A，only then才cái B = "only if A, (then) B": A is the one and only condition.
• only then才cái goes after the subject of the second clause, often with can能néng or can / will会huì.

only if只有zhǐ yǒua lot多duōpractise练习liàn xí，only then才cáican能néngspeak well说好shuō hǎo。

Only this person, only this way

• With a person: only if只有zhǐ yǒuhe他tāonly then才cáiknows知道zhī dàothe answer答案dá àn。 — "Only he knows the answer."
• With a method: only if只有zhǐ yǒu坐飞机zuò fēi jī，talent才能cái néngtoday今天jīn tiānto / arrive到dào。 — "Only by flying can we arrive today."

only只有zhǐ yǒuhe他tā(then)才cáiknows知道zhī dàothe answer答案dá àn。

only then才cái, not then就jiù

only if只有zhǐ yǒu…only then才cái versus as long as只要zhǐ yào…then就jiù

• only if只有zhǐ yǒu A only then才cái B: A is necessary — no A, no B.
• as long as只要zhǐ yào A then就jiù B: A is enough — easy: as long as只要zhǐ yàohave有yǒua passport护照hù zhào，then就jiùcan能néngbuy a ticket买票mǎi piào。 — "All you need is a passport to buy a ticket."

as long as只要zhǐ yàohave有yǒua passport护照hù zhào，then就jiùcan能néngbuy a ticket买票mǎi piào。

Recap

Read the full reference: HSK 3 grammar — Conditional statements.