I have read the following sentences:

Sono un fotografo da molti anni e ho fatto foto in quattro continenti, ma non sono mai stato in una grotta. Credo che siano pericolose!

However, I can't understand why una grotta becomes plural in Credo che siano pericolose! I understand it is a subjunctive form since it is after credere, but i don't understand why it is changed to plural.

Why does it happen?

  • «I never was in a cave. I believe they are dangerous!» doesn't sound too strange in English either (or does it? English isn't my first language).
    – DaG
    Commented Dec 26, 2016 at 0:09
  • Because the subject of the sentence "siano pericolose" is "le grotte", in plural.
    – Charo
    Commented Dec 26, 2016 at 8:33

1 Answer 1


What this photographer is trying to say is that he believes that the caves, all the caves in general, are dangerous. For this reason the subject of the the verb "siano" is "le grotte", in plural. The sentence is

Credo che le grotte siano pericolose!

which, omitting the subject "le grotte" becomes

Credo che siano pericolose!

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