since和for，as，because的区别

because, as, for, since这几个词都是表示“原因”的连词，语气由强至弱依次为：because→since→as→for;其中because, since, as均为从属连词，引导原因状语从句；而for 是并列连词，引导并列句。
　　1. because表示直接原因，它所指的原因通常是听话人所不知道的，其语气最强。常用来回答why的提问，一般放于主句之后，也可以单独存在。例如：
　　(1)I stayed at home because it rained. 因为下雨我呆在家里。
　　(2)Because Lingling was ill, she didn”t come to school. 玲玲因病，没有上学。
　　(3)�Why is she absent? 她为什么缺席？
　　�Because she is sick. 因为她病了。
　　此外，在强调句型中，只能用because。例如：
　　(4)It was because I missed the early bus that I was late for school. 我上学迟到是因为我没有赶上早班汽车。
　　2. since侧重主句，从句表示显然的或已为人所知的理由，常译为“因为”、“既然”，语气比because稍弱，通常置于句首，表示一种含有勉强语气的原因。例如：
　　(1)Since he asks you, you”ll tell him why. 他既然问你，那就告诉他为什么吧。
　　(2)Since everyone is here, let”s start. 既然大家都到齐了，我们就出发吧！
　　(3)Since I understood very little Japanese, I couldn”t follow the conversation. 我日语懂得不多，因而听不懂对话。
　　3. as是常用词，它表示的“原因”是双方已知的事实或显而易见的原因，或者理由不是很重要，含义与since相同，但语气更弱，没有since正式，常译为“由于，鉴于”。从句说明原因，主句说明结果，主从并重。例如：
　　(1)We all like her as she is kind. 我们都喜欢她，因为她善良。
　　(2)As I had a cold, I was absent from school. 因为我感冒了，所以没去上课。
(3)As Xiaowang was not ready, we went without him. 由于小王没有准备好，我们只好不带他去了。
　4. for用作连词时，与because相似，但它所表示的原因往往提供上文未交待过的情况。for不表示直接原因，表明附加或推断的理由，因此for被看作等立连词，它所引导的分句只能放在句子后部(或单独成为一个句子)，并且前后两个分句间的逻辑关系不一定是因果关系，其间用逗号隔开，且for不可置于句首，for的这一用法常用在书面语中，较正式。例如：

　(1)The days are short, for it is now December. 白天短了，因为现在已是十二月份。
　　(2)It must have rained, for the ground is wet. (从“地面潮湿”作出“下过雨”的推测，但地湿并不一定是下雨所致, for不可以换为because。)
(3)The ground is wet because it has rained. (“下雨”是“地上潮湿”的直接原因。)
前后两个分句间有一定的因果关系时(有时很难区分是直接原因，还是推测性原因)，for与because可以互换使用。例如：
　　(4)I could not go, for / because I was ill. 我没能去，是因为我病了。
　　(5)He felt no fear, for / because he was a brave boy. 他没有害怕，因为他是个勇敢的男孩

　　because
　　because引导语气最强，表示直接原因,常用来回答由why提出的问题，所引导从句可放在主句前，也可放在主句后。例如：
　　"Why did you do it?" "Because Carlos told me to".
　　We can't go to Julia's party because we're going away that weekend.
　　Because he didn't catch the last bus, he had to walk home.
　　Why are you late for school ? Because I missed the first bus.
　　
　　as
　　as “由于,鉴于” 主从并重，从句说明原因，主语说明结果。说明比较明显的原因。多用于日常语中，常译为“由于”，从句一般放于主句前。例如：
　　You can go first as you're the oldest.
　　As you don't feel well, you had better stay at home.
　　As he wasn't ready , we went without him.
　　I must stop writing now, as I have rather a lot of work to do.
　　As it was getting late, I decided to book into a hotel. As it is raining, you'd better take a taxi.
　　
　　since
　　since “因为,既然” 侧重主句，主句表示显然的或已知的理由。强调说话者和听者双方都知道的原因，常译为“既然”，一般用在这样的句子里。例如：
　　Since we've got a few minutes to wait for the train, let's have a cup of coffee.
　　Since you are not feeling well, you may stay at home.
　　Since everybody is here, let's begin the meeting.
　　Since I am a boy, let me carry the case.
　　Since/As you are busy, you had better not go with us.
　　Since we have no money, we can't buy that vase.

　　for
　　for “因为,由于”表明附加或推断的理由，引导的分句前常有逗号。for分句不放句首.是用来附带解释或说明前一分句的原因和理由。例如：
　　Day breaks, for the cock crows.
　　It must have rained last night, for the ground is wet.
　　I won't go in, for my father is there.
　　He must be ill, for he is absent.
　　I went to see him, for I had something to tell him.本回答被提问者和网友采纳

since, as because,for都可表示原因，它们的区别是：

1. Becasue：当原因作为句子或陈述最重要的一部分时，我们使用because.
Because通常出现在句首部分。
Because is used when the reason is the most important part of the sentence or utterance. The because clause usually comes at the end:
e.g. I went to Spain last summer because I wanted the guarantee of sunshine on every day of my holiday.

2. As和since：当原因是众所周知时，我们使用as和since，因此，这样的原因一般不那么重要。
as或since从句一般置于句首。
As and since are used when the reason is already well known and is therefore usually less important. The as or since clause is usually placed at the beginning of the sentence:
e.g. As the performance had already started, we went up to the balcony and occupied some empty seats there.
e.g. Since John had already eaten, I made do with a sandwich.

3. For：For意味着原因是事后给出的。
For从来都不会置于句首，带有书面英语而非口语的色彩。
For suggests that the reason is given as an afterthought. It is never placed at the beginning of the sentence and is more characteristic of written, rather than spoken English:
e.g. I decided to stop the work I was doing - for it was very late and I wanted to go to bed.

, because, since, for用法区别

前三者引导原因状语从句，for引导的则为并列句。

as表示明显原因，语气较because强，例如：

As it is raining, we’ll stay (at) home.

because表示内在的、必然的因果关系，语气较强，例如：

He has to leave because it is too late.

since表示鉴于某种既定事实而为之，语气较弱，例如：

Since everyone is here, we can begin our lesson.

for只是作为补充说明，不用于某种结果之前，表示判断某种情况的因素，语气较because弱，但较为郑重、正式，不能放在句首，例如：

I’ll stay home, for I must wait for a friend.

since, as because,for都可表示原因，它们的区别是：

1. Becasue：当原因作为句子或陈述最重要的一部分时，我们使用because.
Because通常出现在句首部分。
Because is used when the reason is the most important part of the sentence or utterance. The because clause usually comes at the end:e.g. I went to Spain last summer because I wanted the guarantee of sunshine on every day of my holiday.
2. As和since：当原因是众所周知时，我们使用as和since，因此，这样的原因一般不那么重要。
as或since从句一般置于句首。
As and since are used when the reason is already well known and is therefore usually less important. The as or since clause is usually placed at the beginning of the sentence: e.g. As the performance had already started, we went up to the balcony and occupied some empty seats there.e.g. Since John had already eaten, I made do with a sandwich.
3. For：For意味着原因是事后给出的。
For从来都不会置于句首，带有书面英语而非口语的色彩。
For suggests that the reason is given as an afterthought. It is never placed at the beginning of the sentence and is more characteristic of written, rather than spoken English:e.g. I decided to stop the work I was doing - for it was very late and I wanted to go to bed.