Cause
Because and because of are used to express the cause of an event or state.

Because is a conjunction, so it must be followed by a finite clause, for example:
Edinburgh attracts a lot of visitors during the summer because the festival is very popular.

Because of is a compound preposition (‘compound’ means that it consists of more than one word). It is most often followed by a noun phrase:
Many people prefer cities to the countryside because of the night life.

Because of can also be followed by a clause beginning with a wh- word, usually what:
I visited the museum because of what I’d been told about it.
A more formal alternative to because of is on account of.

Purpose
The purpose of an action (that is, what is hoped for as a result of the action) can be expressed by using so that (usually so in informal language). It is followed by a finite clause, often containing could or would.
I booked a hotel room in advance so (that) my friends could meet me there as soon as I arrived.
Notice that in this example, the two subjects (I and my friends) are different, and that we don’t know whether my friends met me or not: all we know is that that was my purpose, or intention.

Result
Unlike a purpose, a result is something that actually happens. It can be expressed with so (not so that). It is a conjunction and is followed by a finite clause.
All the hotels seemed to be full, so I stayed in a youth hostel.

Be careful not to confuse the purpose and result meanings of so.
I booked a cheap hotel at a distance from the city centre so I could save money, but I spent a lot on taxis, so I didn’t save anything.
The first so introduces a purpose, and the second one introduces a result.

In more formal language, results are usually expressed in other ways, such as:
The city’s advertising campaign led to / resulted in a big increase in the number of tourists.
The main bridge across the river was closed, with the result that traffic came to a standstill.


These activities practise this Grammar: