Since (given that): 既然……就
复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
既然 (jìrán) = "since, now that". The first part is a fact already known or accepted by both speakers; the second draws a conclusion, often advice or a decision, introduced by 就 (or 也, 还).
Difference from 因为: 因为 gives a new cause; 既然 starts from an established fact to draw a consequence: 既然你不舒服，就别去上课了 (since you're unwell, as we both know, don't go to class).
Examples
既然你喜欢画画，就去学美术吧。
Jìrán nǐ xǐhuan huàhuà, jiù qù xué měishù ba.Since you like drawing, why not study art?
既然已经决定了，就别后悔。
Jìrán yǐjīng juédìng le, jiù bié hòuhuǐ.Now that you've decided, don't regret it.
既然考试结束了，我们就好好儿休息几天。
Jìrán kǎoshì jiéshù le, wǒmen jiù hǎohāor xiūxi jǐ tiān.Since the exams are over, let's have a good rest for a few days.
Common mistakes
✗ 既然……所以…… → 既然 pairs with 就. ✓ 既然……就……
✗ Using 既然 for new information: ✗ 既然我头疼，所以没来 (explaining a cause) → ✓ 因为我头疼，所以没来。