Impersonal passive

IMPERSONAL PASSIVE
a) It is a special case of passive, commonly associated with reporting verbs, that is verbs of saying and thinking: think, believe, say, report, know, consider, presume, hope…. These verbs are often followed by a to-infinitive form in the passive.
These types of sentences are very common in newspapers and TV news, and more colloquially, when someone is gossiping.
Ex.: Active- The police think the terrorists are in France.
Passive- The terrorists are thought to be in France.
b) How have we done this?
1. We take the subject of the second sentence (the terrorists)
2. We make the reporting verb think (simple present) passive in the same tense as in the active: are thought (simple present passive).
3. Finally, the verb of the second sentence (are) becomes infinitive: to be.
Or we introduce “It” as the subject of the passive verb and keep the rest of the active sentence: It is thought that the terrorists are in France.
c) Which form of the infinitive shall we use?
There are four infinitive forms depending on the tense of the active sentence.
1. Simple to write
2. Continuous to be writing
3. Perfect to have written
4. Perf. Cont. to have been writing

1. If it carries an idea of present or future: Simple: to be.

2. If it carries an idea of past, whatever the tense (Past Simple, Past Perfect, Present Perfect): Perfect: to have escaped.
3. If either of them is in a continuous form, use the adequate cont.form: to be writing or to have been writing.
Ex: The terrorists are thought to be hiding in a flat (now).
They are also thought to have stolen a big amount of explosives from a mine (some time ago).
d) Some verbs have special passive forms:

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