Some verbs (you just have to learn which ones) can have their object before them as a subject without changing to the passive voice
DEFINITION OF PASSIVE VERBS
Many English verbs can have what is called the “passive” form, in which they are given the “past participle” ending (-ed or irregular equivalent – see 52. Participles Placed Just After their Noun) and placed after some form of BE. Examples (with the BE part underlined) are was helped, is understood, were being copied, can be taken and should have been known. Sometimes BE is replaced by BECOME or informal GET, e.g. got taken.
THE NORMAL USE OF PASSIVE VERBS
We normally learn that when a verb is in the passive form, the noun written before it as subject would have been the object of the same verb in the active form (for a discussion of objects, see 8. Object-Dropping Errors). Take the verb ENJOY. Its normal objects are nice things that affect people’s emotions, like ice-cream or music. Its typical subjects are people, or other living things that can feel emotions. Consider this sentence beginning with a typical object of this verb:
(a) The reward ……………….
If we wish to use the verb ENJOY here, we will need to make it passive because of its typical object being first, e.g. was enjoyed. We can then choose to include or not include the subject, say the children, by placing it after the verb with by in front: … by the children.
Here is another example:
(b) ………… is assisted by ………… .
If we wanted to mention two nouns here, sunshine and plant growth, which one would have to be first because the verb is passive? The answer is plant growth, because only that could be a logical object of ASSIST. More about the meaning of the passive form is in the posts 21. Active Verbs with Non-Active Meanings 1 and 66. Types of Passive Verb Meaning.
VERBS THAT BREAK THE PASSIVE RULE
What we do not often hear is that some verbs do not follow these rules, and can be in an active form even when their typical object comes first. In other words, they can nearly always be active. Consider this:
(c) Obesity is increased by overeating.
(d) Obesity increases with overeating.
Changing the verb here from passive to active does not also require a change of word order. The only other visible change is in the preposition after the verb (from by to with). We could instead have used through or as a result of, but not by.
There is actually a meaning change too: the passive in sentence (c) clearly says overeating is the cause of obesity, while the active in (d) does not, simply saying instead that it happens at the same time. The passive would be preferred where there was a need to emphasise the causal role of what is said or implied after it, but this need is probably not very frequent or important.
A key point to appreciate is that only some verbs can be kept in the active form regardless of what their subject is, like INCREASE. The verbs ASSIST and ENJOY are not among them. This raises the question of which verbs are like INCREASE and which are like ASSIST and ENJOY, and whether there is any rule for recognising them.
Unfortunately, this is a similar problem to that of whether a noun is countable or uncountable (see 23. Countable Noun Meanings 3: Subtypes): there is no definite rule that might help, but sometimes the meaning of the verb is a guide. Many verbs of “change and motion” are like INCREASE. Among those, verbs of starting and ending are especially reliable, e.g. START, BEGIN, COMMENCE, OPEN, END, FINISH, TERMINATE, STOP, HALT, CLOSE and CEASE.
Quite often, verbs that in other European languages include a -self word are like INCREASE in English (see 143. Problems Using “-self” Words). Examples are ADVANCE, AWAKEN, IMPROVE, MOVE and TURN. Some less reliable meanings – and errors that can result – are illustrated in the post 142. Reasons for Passive Verb Errors.
The surest way to know whether or not a particular verb is like INCREASE is to check it in a dictionary. Verbs of this kind are labelled “vt and vi” (verb transitive and intransitive). In comparison, verbs like ASSIST, which cannot directly replace their passive form with an active, are usually just labelled “vt”. Verbs like INCREASE, with which the passive is possible but avoidable, should not be confused with verbs that cannot ever be passive (verbs labelled “vi” – verb intransitive – in dictionaries), such as GO. More about these is in the post 113. Verbs that Cannot be Passive.
One verb that needs a special mention is BENEFIT. It is similar to INCREASE, but not quite the same. Here is a normal active use:
(e) Exercise benefits everyone.
If we rewrite this sentence with the object first, we still use the active voice of the verb, followed by a preposition that is not by:
(f) Everyone benefits from exercise.
What is different is that BENEFIT is not so much a verb that can always be used in the active voice as one that should be. It would sound a little strange to say is benefited by in (f).
The following exercise, from my coursebook Grammar Practice for Professional Writing, can be used to find out how easily you can recognise verbs like INCREASE. For a more academic article on the general use of the passive voice in English, please click here.
PRACTICE EXERCISE (Unnecessary Passives)
Test your vocabulary knowledge by identifying the sentences below whose passive verb could also be active (followed by a different preposition from by), without a change in word order. Answers are given afterwards.
1. Reading speeds are improved by constant practice.
2. A new academic term is usually begun in January.
3. Many commercial aircraft are flown across the Atlantic every day.
4. The Pacific is crossed by aircraft on a regular basis.
5. The countries of SE Asia are being rapidly developed.
6. Attitudes can be changed by education.
7. Heat can be transferred by means of radiation.
8. Clouds are formed from water vapour in the atmosphere.
9. Africa was opened up in the nineteenth century.
10. The destruction of forests will be continued in the future.
11. Much business efficiency was gained by computerisation.
12. Scientific knowledge is being widened all the time.
13. Metals are expanded as they are heated up.
14. Electrical resistance is decreased by use of suitable materials.
15. It is worrying to see forests being destroyed.
16. Cars are driven on the left of the road in Japan.
All of the verbs can also be used in the active without a word order change except those in sentences 4 (cross), 11 (gain) and 15 (destroy). The rewritten sentences might look like this:
1. Reading speeds improve WITH constant practice.
2. A new academic term usually begins in January.
3. Many commercial aircraft fly across the Atlantic every day.
5. The countries of SE Asia are rapidly developing.
6. Attitudes can change WITH education.
7. Heat can transfer by means of radiation.
8. Clouds form from water vapour in the atmosphere.
9. Africa opened up in the nineteenth century.
10. The destruction of forests will continue in the future.
12. Scientific knowledge is widening all the time.
13. Metals expand as they heat up.
14. Electrical resistance decreases by use of suitable materials.
16. Cars drive on the left of the road in Japan.