既然…就…
Since (given that)…, then…
HSK 4HSK 3.0 · 4
既然 + known fact，(S) + 就/也/还 + suggestion/conclusion
既然 states a fact both parties already know, and the second clause draws a conclusion or makes a suggestion: 既然你不舒服，就早点儿回家吧 'since you're not well, go home early'. Unlike 如果 (an unverified hypothesis) and 因为 (objective cause–effect), 既然 is about reasoning. The second clause is often a suggestion, command or rhetorical question, with 就/也/还 after the subject.
HSK 4–5 gap fills, often alongside 如果 and 即使.
Examples
既然你不舒服，就早点儿回家休息吧。
Since you're not feeling well, go home and rest.
既然已经决定了，就别再后悔了。
Now that it's decided, don't regret it.
既然大家都同意，我们就这么办。
Since everyone agrees, let's do it this way.
既然你知道错了，为什么不改呢？
If you know you were wrong, why not change?
Exercises
1. 你已经来了，就一起吃饭吧。
2.既然你不喜欢， 别买了。
3.（It is not yet known whether it will rain tomorrow） 明天下雨，我们就不去了。
4.既然大家都没意见，那我们 开始吧。