As, Because and Since (reason)

As/because/since + clause + clause Clause + As/Because/Since + clause

1.       Because is used when we give the reason for something

Because I was ill for six months I lose my jobs

If the reason is the most important idea, we put it at the end  of the sentence

Why am I leaving? I am Leaving because I am fed up!

2.       As and Since are used when the reason is not the most important idea in the sentence, or when it is already known. Since is more formal.

As- and Since-clauses often come at beginning of then sentence.

As it’s raining again, we shall have to stay at home;

Since he had not paid his bill, his electricity was cut off.

As if and as though

take from : basic english usage by Michael Swan

as if/though + subject + present/past verb as if/though + subject + past verb with present meaning

1. As if and as though mean the same.

We use them to say what situation in seem like

It looks as if/though it’s going to rain

I felt as if/though I was dying

2. We can use a past tense with a present meaning after as if/though. This means that the idea is “unreal”.

Compare:

He looks as if he’s rich (Perhaps he is rich)

She talks as if she was rich (but she isn’t)

We can use were when express “unreal” idea after as if/though. This is common in a formal style.

She talks as if she was rich

3. Like is often used instead of as if/though, especially in American English. This is very formal.

It looks like it’s going to rain.