Purpose in English: For, To or So That?

Remember: To talk about purpose, or the reason why we do things, we can use for + verb-ing,  
the infinitive with to
so that + subject + verb.

Examples:
Action or event 'for' + verb-ing 
I'm bringing some pots and pans for cooking.
I've got special glasses for reading small print.
A thermos flask is for keeping hot food hot.

Action or event Infinitive with 'to'
We've got some water to make tea.
I went to the shops to buy some milk.
I worked very hard to get a promotion.

Action or event 'so that' + subject + verb
I'm taking some extra blankets so that we don't get cold.
I chained my bicycle to the fence so that it wouldn't get stolen.
I worked very hard so that I would do well in the exam.

Practise in these quizzes: Quiz 1 quiz 2