Infinitive of Purpose and For
This is quite a simple grammar point but many students still seem to make this mistake so it is worth a review.
When we want to use an ACTION and a REASON in the same sentence we will often use an infinitive (to + verb)
Action Present: I go to the shop
Reason: to buy milk
Action Past: I moved to China
Reason: to improve my Chinese
Action Future: I will study abroad
Reason: to gain more qualifications
Notice – the reason always uses the present tense.
What about for?
We can also use for with a noun to describe a reason in a sentence.
Action Present: I go to the shop for milk
Action Past: I went to the shop for milk
Action future: I will go to the shop for milk
Notice – We CANNOT use for + verb – I went to the shop for to buy milk
For + Verb ing
We can also use this structure to show what the use of an object is, not a reason. This is a common mistake I see
A knife is for cutting – correct
This describes what a thing can do, or its function, not an action
I go to the shop for buying milk – incorrect
This describes a reason for an action, so we should use ‘to buy’ milk
In order / So as
In more formal situations we often use these to replace before ‘to’
Present Action: She reads a lot in order to gain new knowledge
Past Action: I went to America so as to gain a deeper understanding of western culture
Future Action: He will continue his studies in order to improve his life
Notice – Only use this with more formal language and when writing. Nobody will say – ‘Yesterday I went to the shop in order to buy milk’