Active verbs in the infinitive form (with “to”) can have passive meaning after some adjectives and verbs
THE ABILITY OF ACTIVE VERBS TO HAVE A PASSIVE MEANING
It is very possible for an active verb to have a passive meaning. One of the ways in which this can happen is through the very meaning of the active verb – more “passive” than “active”. This possibility is considered in the post 21. Active Verbs with Non-Active Meanings 1. Examples of such verbs are SUFFER and RECEIVE, or CHANGE and START used without an object.
In other cases, it is special preceding words that give an active verb a passive meaning. These can affect practically any verb. In this post, I wish to examine two types of preceding words that can give a passive meaning to a verb in the active form. One type is adjectives of a certain kind, the other a small number of special verbs.
ADJECTIVES FOLLOWED BY ACTIVE VERBS WITH PASSIVE MEANING
There are quite a lot of adjectives that can give a passive meaning to a following active verb, but many that cannot. Those that can are illustrated in sentence (a) below, the others in (b):
(a) Foreign languages are useful to know.
(b) Foreign languages are sure to fascinate.
Sentence (a) is special because the verb at the end can also go at the start (Knowing foreign languages is useful). Doing this with (b) only creates nonsense (*Fascinating foreign languages is sure). Grammatically speaking, foreign languages is the object of know in (a), but not the object of fascinate in (b) (which is instead something unmentioned like people). For more on objects see 8. Object-Dropping Errors. The words that cause the meanings to vary in this way are respectively the adjectives useful and sure.
One reason for saying that to know in (a) has passive meaning is the fact that its object foreign languages is placed before it, just as is the case with ordinary passive verbs. Another is that speakers of other languages often incorrectly give it the passive form (to be known), presumably because they are directly translating from their mother tongue (rather than being influenced by any of the factors mentioned in 142. Reasons for Passive Verb Errors).
Against this, some might argue that to know is only superficially passive, since the words for people can be added just before it (for people to know …) giving it an active but otherwise unchanged meaning.
There are some fairly noticeable characteristics of sentences containing a passive-seeming verb like know in (a):
(i) The verb will be in the “infinitive” form with to.
(ii) The verb will be “transitive”, i.e. normally requiring an object noun or pronoun after it (see 8. Object-Dropping Errors).
(iii) There will be no noun or pronoun in the “object” position after the verb.
(iv) The adjective before the verb will describe the subject of the sentence – foreign languages in (a). In other words, it will be a “complement” of that subject, separated by a link verb like BE.
The list of adjectives like useful is very similar to one given already in another part of this blog (78. Infinitive versus Preposition after Nouns) in order to illustrate a different point. This was that nouns related to them (e.g. usefulness) need any verb following directly after them to be in the -ing form with of or another preposition in between, rather than in the to form. A new list is needed here because that one includes a few adjectives that are slightly different from useful, and it is not very comprehensive.
Below is a more comprehensive list of adjectives that can go before an active to verb of passive meaning. I have broken it into four shorter lists in order to make it easier to remember and perhaps more interesting to read. The shorter lists indicate four basic meanings that adjectives of this kind appear to have:
Meaning 1: Usefulness
Meaning 2: Ease/Difficulty
Meaning 3: Danger
Meaning 4: Enjoyability
In case it is thought that the majority of adjectives can take an active to verb with passive meaning, here are some more examples of those that cannot: ABLE, AFRAID, ASHAMED, CAREFUL, CERTAIN, CURIOUS, FORTUNATE, KEEN, LUCKY, RIGHT, WRONG, WILLING. Note also that READY can be used in two different ways:
BEFORE A PASSIVE MEANING
(c) After two practices, the students will be ready to test.
BEFORE AN ACTIVE MEANING
(d) After two practices, the students will be ready to write.
The ability of a single structure to be understood in two different ways is considered in more depth in the post 124. Structures with a Double Meaning.
Finally, there is a need for care with worth. Although it can express meaning type 1 above (“useful”, “valuable” etc.), and it gives passive meaning to any directly-following active verb, that verb needs -ing instead of to:
(e) Language exercises are very worth doing.
The reason for this difference is that worth is actually a preposition, not an adjective, and hence like all prepositions only allows following verbs with -ing (see 84. Seven Things to Know about Prepositions). An adjective equivalent of worth is worthwhile, but this too needs -ing not to.
The suggestion is made elsewhere within these pages that words with different grammar from that of most other words with similar meaning are likely to be used incorrectly (see 10. Words with Unexpected Grammar 1), and worth is certainly one of them, being often incorrectly linked with a following to verb. This error is made even more likely by the fact that saying worth it instead of worth alone does actually need a following to verb (see 165. Confusions of Similar Structures 2, #2).
VERBS FOLLOWED BY ACTIVE VERBS WITH PASSIVE MEANING
The number of verbs that give passive meaning to a following active verb is very small. They are essentially NEED, WANT, DESERVE, MERIT and REQUIRE. The subsequent verb mostly has to be in the -ing form (see 70. Gerunds), like this:
(f) Small children need supervising at all times.
When WANT is used in this way with a following -ing verb, it means “need” rather than “desire”. It is also a very conversational use, not recommended in writing of a more formal kind (as defined in the post 46. How to Avoid “I”, “We” and “You”).
Two of the four verbs, NEED and DESERVE, can also go before a passive to form (e.g. need to be supervised). This option is preferred in writing of a more formal kind. WANT is also found with a following passive to form, but only with the meaning of “desire”. REQUIRE and MERIT must always be used with a following -ing form (see 65. Verbs that Mean “Must” or “Can”).