Expressing purpose: TO+inf or FOR+-ing

Cuando expresamos un propósito + verbo (para + verbo) solemos utilizar TO + inf. en la mayoría de los casos. Pero a veces dudamos si expresarlo mediante FOR + -ing. 

We must understand the usage of “to verb” and “for verb” to be able to distinguish between the contexts where these phrases can be used correctly.

Use of “to verb" – This phrase is used when we need to present the purpose or the intention of an action. This phrase is actually a shorter way of “writing” “in order to verb”. Let’s take the simple sentences with this phrase we mentioned in the beginning of the article.

1.            Joe wrote a book to share his experiences with others: This sentence correctly uses “to share” because it presents the purpose why Joe wrote the book. It is explicit from the context that Joe wrote the book because he wanted to share his experience with others.

2.            Joe got acclaims to write the book: This sentence does not use “to write” correctly because writing the book is certainly not the purpose of Joe getting acclaims.

Use of “for verb-ing” – Since “for” is a preposition, it can modify either a noun or a verb. Prepositional phrase “for verb-ing” can modify the verb or the noun in that it denotes some relation to the entity it modifies. Let’s understand this through the previously mentioned simple sentences.

1.            Joe got acclaims for writing the book: This sentence correctly uses “for writing” because this prepositional phrase logically modifies the verb “got”. Here, there is no question of presenting any purpose. The sentence rather explains “what for” Joe got acclaims. Hence, use of “for writing” is correct.

2.            Joe wrote a book for sharing his experiences with others: This sentence incorrectly uses “for sharing” to denote Joe’s intention of writing the book.




for or to + infinitive: individual purpose
For is commonly used with nouns to express individual purpose:

I popped into the supermarket for some apples on the way home.
(Not: I popped into the supermarket for buying some apples…)

I stopped by at his office for a chat about our marketing strategy.
(Not: I stopped by at his office for having a chat about marketing.)

I decided I would save up for a new computer.
(NOT: I decided I would save up for buying a new computer.)

If we want to express individual purpose with a verb pattern, we are obliged to use to + infinitive:

I stopped by at the supermarket to buy some apples on the way home.

I popped into his office to have a chat about our marketing policy.

I decided to save up to buy a new computer.

                               
For + verb-ing: the purpose of an object

However, if we are talking about the purpose of an object or an action, we normally use the for + verb-ing pattern. Note that this pattern commonly answers the question: What are they (used) for? Compare the following:

Schools are for educating children not for entertaining them.

Schools are for learning. Life is for living.

This kitchen knife is especially useful for slicing vegetables.

What's this for? ~ It's for opening oysters. It's much better than a knife.

What's this fifty pound note for? ~ It's for buying food for the weekend.

Note that when the subject of the sentence is a person rather than the thing described, the to + infinitive pattern is also possible:

I use this small knife to slice vegetables with.

I use this gadget to open shellfish with.

                                                              
                               
in order to / so as to

Note that, as an alternative to to + infinitive, we might use in order to, or so as to, to express individual purpose when we want to be more formal or explicit about the reason for doing something. All of these structures answer the question: Why…?. Compare the following:

I went to bed early in order to get enough sleep before the exam.

After four weeks of exams, I went to the seaside to rest.

After twenty days of exams, I went to the seaside for a rest.

After all those exams, I went to the seaside so as to have a good rest.

The in order to and so as to structures are particularly useful with stative verbs such as be, have, know, appear, and before negative inifinitives:

So as not to appear foolish, I learnt all I could about the company before going for the interview.

I'm going to move to the city centre in order to be near where I work.

In order not to have to commute, she bought a flat in the town centre.


In order to know more about him, she studied his movements carefully.


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