The word “for” acts differently in different kinds of purpose sentence, and sometimes causes errors as a result
THE PROBLEM POTENTIAL OF PURPOSE-SHOWING “FOR”
Purpose sentences often contain the preposition for. However, there are some rather confusing rules concerning this word in purpose sentences, and as a result some common errors made with it. A particularly noticeable error is combining for with an -ing verb, like this:
(a) *Afterwards the dancers go off for enjoying themselves.
Although an -ing verb can sometimes be used after for to express a purpose, it cannot in this example sentence. The underlined words should be either to enjoy, in order to enjoy or so that they can enjoy. In this post I wish to examine exactly when you can and cannot use for in a purpose sentence.
THE BASIC FEATURES OF PURPOSE SENTENCES
Purposes are future events or situations that living creatures want to achieve by doing things. Consider these examples:
(a) Doctors STUDY anatomy so that they MAY UNDERSTAND sickness.
(b) Colleges TEACH anatomy so that doctors WILL UNDERSTAND sickness.
The underlined words are purposes. The living creatures that want to achieve them are doctors in (a) and colleges in (b). The things being done to achieve the purposes – what we might call the “means” of achieving them – are shown by the words that are not underlined.
In most cases, both the means and the purpose are expressed with a verb (for an exception, see 119. BE before a “to” Verb). Each of the two verbs needs its own subject (the post 12. Singular and Plural Verb Choices explains what subjects are). In (a), the two subjects are the same (doctors), so that the second mention is made with a pronoun (they), which cannot be left out (see 36. Words left Out to Avoid Repetition). In (b), the two subjects are different (colleges, doctors).
The words so that before the purpose in (b) are a conjunction (they allow the sentence to have two verbs). An alternative purpose conjunction is the slightly more formal in order that. With these conjunctions, the purpose verb must usually contain can, will or may or their “past” equivalents could, would or might (see 32. Expressing Consequences).
Three other synonyms of so that are to, in order to and so as to. However, because they have to instead of that, their following verb cannot contain may etc. They also need their subject to be expressed differently. Compare:
BOTH SUBJECTS THE SAME WITH “to”
(c) Doctors study anatomy (in order/so as) to understand sickness.
Here, the repeated subject is left out – using they is not possible.
BOTH SUBJECTS DIFFERENT WITH “to”
(d) Medical colleges teach anatomy (in order) for doctors to understand sickness.
In this case, the different second subject (doctors) has to be mentioned. It needs for because the verb has to. Note that so as to cannot replace to.
The use of for in (d) illustrates what is probably its most important one in purpose sentences. It can be summed up like this:
1. For and its noun go directly before to.
2. The noun expresses the subject of the to verb, not the purpose itself.
3. The to verb’s subject is not the same as the other verb’s subject.
OTHER USES OF “for” IN PURPOSE SENTENCES
In other uses, for is more associated with the purpose itself than its subject. There seem to be two different kinds of use: one with a noun and no verb after for, and one with a verb and no noun (a noun and verb together can only be the use described above).
1. “For” + NOUN meaning “in order to get”
English quite often uses for + NOUN to mean either “in order to obtain”, “in order to receive” or “in order to have”. In these cases, the noun after for shows what the purpose holder wants to get. Here are some examples:
(e) Students have to work hard for good grades.
(f) The patient needs to return to the clinic for a reassessment.
(g) For a full explanation, please turn to page 6.
(h) It is healthy to go for regular walks.
Although no verb appears with this use of for, the fact that one is likely to be used in a paraphrase shows that a verb idea is still present. Note that using an -ing verb after a for with this meaning (*for getting, *for obtaining, *for receiving, *for having) is nearly always wrong. The only possible use of -ing is without for after some uses of go (go walking, go swimming, go dancing etc. – see 165. Confusions of Similar Structures 2, #3).
2. “For” + VERB + “-ing” meaning “in order to do” (certain verbs only)
Expressing “in order to do” with for + -ing only seems possible when the main verb in the sentence is one of a small group, of which the most common is perhaps USE. Here is a typical purpose sentence containing USE:
(i) An ammeter is used for measuring electric current.
Instead of an -ing verb, one could also use an “action” noun (the measurement of … – see 131. Uses of “Action” Nouns). The passive form (is used) seems especially common in such sentences, but is not universal. The active is certainly possible too in (i) (We use an ammeter …). It may in general be more of a possibility in statements that, like (i), are true of all times rather than of particular occasions.
Other verbs which allow for + -ing meaning “in order to do” are HAVE, KEEP, NEED and ALLOW, as well as their synonyms (e.g. POSSESS, MAINTAIN, STORE, REQUIRE and PERMIT). Adjectives related to them can also be used in combination with BE. Common examples are USEFUL, OF USE, VALUABLE, HELPFUL, GOOD, SUITABLE, NECESSARY, OPTIONAL, REQUISITE, IMPORTANT, VITAL, ESSENTIAL, CRUCIAL, COMPULSORY and MANDATORY
A NON-PURPOSE USE OF for + -ing
If for + -ing is used with other verbs, including BE by itself, it will either sound incorrect or express a function rather than a purpose. Functions name what something does, rather than what people hope it will do (see 119. BE Before a “to” Verb). Consider this:
(j) Chlorophyll in plants is for utilizing solar energy.
Chlorophyll here is not consciously trying to perform its function.
The function and purpose uses of for + -ing are recognisable from their grammar as well as their meaning. The function usage tends to act like an adjective in sentences, the purpose one an adverb. The ability of preposition phrases in general to act in these two different ways is considered in detail in the Guinlist post 84. Seven Things to Know about Prepositions. Adjective-like uses can be linked with a preceding noun – chlorophyll in (j) – while adverb-like ones cannot, and hence link with a verb – is used in (i).
In (j), the for phrase is separated from its noun chlorophyll by the verb BE. In other cases, however, the noun and for + -ing will be together:
(k) The form has a SPACE for giving extra information.
This names the function of the space in question. If the subject of the sentence is human, for phrases of this kind might instead be understandable as expressing a purpose – but only if the main verb is one of those listed above. In the following example, this is not the case, so again a function rather than a purpose is being expressed:
(l) The Council PROVIDES bins for disposing of rubbish.
Because the main verb here is provides, the underlined words are the function of bins, not the purpose of the Council. In order to change the underlined words into a purpose, one would need to use for in the first way described above: for + NOUN + to + VERB, e.g. … for people to dispose of rubbish.
PRACTICE EXERCISE: “for” IN PURPOSE SENTENCES
Readers wishing to test their understanding and memory of the points above may like to try the following small exercise. The sentences must be judged as grammatical or ungrammatical purpose statements, and corrected where necessary. Suggested answers are given afterwards.
1. Drivers look at a speedometer for knowing how fast they are travelling.
2. Headlamps should be switched on for the vehicle to be visible in fog.
3. It is sometimes wise to sound the horn for safety before a bend.
4. For preventing evaporation, the fuelling pipe needs a cap.
5. Cars have indicators for the driver giving warnings.
6. Switch on the air conditioning for travelling in comfort.
7. For journeys without stress, cruise control is available.
1. Rewrite for knowing as (in order) to know (for + -ing is not possible with the main verb look at).
2. No change (for+ SUBJECT + to+ PURPOSE VERB).
3. No change (for + NOUN = “in order to obtain”).
4. No change (for + -ing with acceptable verb needs).
5. Either delete the driver so as to leave for + -ing after HAVE, or rewrite giving as to give to make for + NOUN + to.
6. Rewrite for travelling as (in order) to travel (for + -ing is not possible with the main verb switch on).
7. No change (for + NOUN = “in order to obtain”).