I have problem with the meaning of following sentence and its grammatical structure.

If they are to be believed

How is this different from

If they are believed

When do we use am/is/are + passive infinitive?

  • 3
    Welcome. I think it would be better to submit three separate questions (or perhaps two because the second is simply an error). Note that, "He'd (he had) took a sick day" is grammatically incorrect -- the past participle of 'to take' is 'taken'. You can say, "He'd taken a sick day" or "He took a sick day." Nov 2, 2015 at 16:17
  • to be believed is a passive infinitive, thus my edit to your question
    – user20792
    Nov 13, 2015 at 13:10

2 Answers 2


The verb "be" is among modal verbs (like "must", "should", "ought", etc.) and used to express a pre-existing agreement or common sense perception of behavior.

We are to arrive to New York terminal at 6:15pm.

meaning: if all goes well, the train/bus will be there at that time, according to the schedule or timetable.

John was to give a lecture on the 16th.

meaning: John was put in charge of giving the lecture (and agreed to do it).

The phrase

If they are to be believed...

means that "If common sense suggests that we/you should believe them..." or that "if, according to some predefined plan or agreement, we/you accept what they are saying as truth..."

In comparison,

If they are believed...

is a supposition of acceptance of "their" statements as true, simple passive voice.

  • Be is a non-modal auxiliary.
    – user230
    Nov 22, 2015 at 23:16

It's a subtle difference, but "If they are to be believed" questions whether someone should believe them, as opposed to whether someone does believe them.

(Admittedly, even that doesn't seem to fully capture the slight difference in intention, but I'm open a better explanation.)

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