既然…就…: since…, then…
复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
既然 + accepted fact，(S) 就 + conclusion
既然 starts from a fact both speakers already know or accept and draws a conclusion, often advice or a decision: "since…", "now that…".
Versus 因为: 因为 gives an objective cause, while 既然 builds on an accepted situation to say what should be done. The second clause often contains 就, 那 (么), 还, or a rhetorical question.
Examples
既然你已经决定了，我就不多说了。
Jìrán nǐ yǐjīng juédìng le, wǒ jiù bù duō shuō le.Since you've already decided, I won't say any more.
既然身体不舒服，就早点儿回家休息吧。
Jìrán shēntǐ bù shūfu, jiù zǎo diǎnr huí jiā xiūxi ba.Since you're not feeling well, go home early and rest.
既然大家都同意，那就这么办。
Jìrán dàjiā dōu tóngyì, nà jiù zhème bàn.Since everyone agrees, let's do it this way.
Common mistakes
✗ 既然明天会下雨… (uncertain) → 既然 needs an established fact. For a hypothesis use 如果.
✗ 既然…所以… → ✓ 既然…就…。所以 pairs with 因为, not 既然.