As as a preposition
We use as with a noun to refer to the role or purpose of a person or thing:
I worked as a waiter when I was a student. Most of us did.
Not: I worked like a waiter …
[The Daily Telegraph is a British newspaper]
The Daily Telegraph appointed Trevor Grove as its Sunday editor.
Internet shopping is seen as a cheaper alternative to shopping on the high street.
A sarong is essential holiday gear. It can be used as a beach towel, wrap, dress or scarf and will take up no space in your bag.
Warning:
We don’t use as + noun to mean ‘similar to’. We use like + noun:
It’s almost like a real beach, but it’s actually artificial.
Not: It’s almost as a real beach …
I would like to have a white cat like the one in my dream.
Not: … as the one in my dream
As as a conjunction
The conjunction as has several different meanings. We use as when one event happens while another is in progress (‘during the time that’). In this case the verb after is often in the continuous form:
They arrived as we were leaving. (time conjunction meaning ‘while’ or ‘when’)
We use as to connect a result with a cause:
I went to bed at 9 pm as I had a plane to catch at 6 am. (reason and result meaning ‘because’)
We also use as to mean ‘in the way that’:
As the forecast predicted, the weather was dreadful for the whole of the weekend.
She arrived early, as I expected.
The same as
We use as with the same to talk about identical things:
Your jacket is the same colour as mine.
As: simultaneous changes
We use as to introduce two events happening at the same time. After as with this meaning, we usually use a simple (rather than continuous) form of the verb:
As the show increases in popularity, more and more tickets are sold daily.
Warning:
We don’t use as alone to introduce examples. We say such as:
They gave them gifts such as flowers and fruit and sang a special welcome song.
Not: … gifts as flowers …