都是表原因，because，as，since和for有啥区别？

Because：侧重原因

【例句】：She spoke quietly because she did not want to wake up the baby.

【翻译】：她小声得说话，因为不想吵醒孩子。（直接的因果，不想吵醒孩子导致说话声音小）

【例句】：Because I am disappointed, I want to go.

【翻译】：因为我失望了，所以我想离开。

As：侧重结果，由于听者所知道的原因

【例句】：Don’t tell me bad things in the morning as it sets the mood for the rest of the day.

【翻译】：大早晨的，别告诉我坏事，因为早晨的心情决定了一整天的心情。

【例句】：As it is raining outside, you’d better stay at home.

【翻译】：外面在下雨，你最好还是呆家里吧。

Since：侧重结果，通as，比as更正式，与其也更强。

【例句】：They are expensive, since their quantity is small.

【翻译】：物依稀为贵。

【例句】：Since people can do many things at home via internet, it is not necessary for them to find a job outside.

【翻译】：既然人们可以在家通过网络做很多事，所以他们无须出去工作。

For：表示推断的原因，或解释说明，只能放句末。

【例句】：He must be at home, for it is raining.

【翻译】：他一定在家，因为下雨呢。 下雨不是必须在家的原因，却是推测的依据。

【例句】：I want to see you, for I miss you.

【翻译】：我想见你，因为我想你。