BBC English Masterclass: Infinitives of purpose

Dan knows that you're here to get better at speaking English, so he has made this short video to help you use infinitives of purpose.
We use infinitives of purpose to explain why we're doing something. Example:
You're watching this video TO GET better at speaking English.
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Transcript:
Hi guys, Dan for BBC Learning English here. In this masterclass we'll be taking a look at infinitives of purpose. Are you ready? Here we go.
To explain why we're doing something
So, in English we use the infinitive of purpose to explain why we're doing a particular action. For example, you're watching this video to get better at speaking English. Am I right? Of course I'm right.
Now, ''to get better at speaking English'' is an example of the infinitive of purpose and it follows the clause and the action which I wish to explain. We can also use for + somebody to explain that we're doing an action on behalf of someone else. For example, I make these videos for you to get better at English. Or, he bought the flowers for her to make her happy. Got it?
To be more formal
To make things more formal, we can use in order to or so as to. For example, "The government has raised taxes in order to fund the NHS", but, "People have taken to the streets so as to protest against the increase in taxes."
Negatives
What's really nice about these expressions is that they can easily be made negative using 'not' - so as not to and in order not to. For example, "He paid the fine in order not to go to prison." Or "I've worked really hard all my life so as not to be poor." Did you get it?
Contrast
OK guys, so we don't use to + the infinitive with 'not'. For example, I wouldn't say "I went to bed not to watch TV." That doesn't make sense. I would prefer to use a different verb to express the negativity. For example ''I went to bed to avoid watching TV''. However, we do use 'not' and the infinitive when we make a contrast with 'but', so for example, "I went to bed not to sleep, but to watch TV." Did you get it?
After nouns and pronouns
Finally, we can use the infinitive of purpose after a noun, pronoun or indefinite pronoun to explain what we need it for. For example, "I want a house to live in." Or, what we intend to do with it, so ''do you have any more food to cook?'' Now in this example, the noun 'food' is the object of the infinitive, which is fine, but we mustn't add an object pronoun afterwards. So don't say ''do you have any more food to cook it?'' That doesn't make sense.
Finally, we can use the infinitive to qualify an indefinite pronoun, so for example ''I need somewhere to stay.'' ''Do you have anything to eat?'' Did you get it? Great guys. For more information check out bbclearningenglish.com. I'll see you next time. Take care.