Here are some words to express why something is done.

to

You can use use ‘to + verb’ to say why we do something.

For example:

I’m going to Ireland to visit my family.

I went to the post office to buy some stamps.

so as to do something

• I went to the post office so as to buy some stamps.
• They usually try to do jobs for cash so as to avoid paying taxes.
• He was blindfolded so as not to reveal the secret

in order to do something

For example:

I’m going to Ireland in order to visit my family.

so that + clause

It is normally followed by modal (e.g. can, will).

For example:

I am saving money so that I can buy a new car.