In the book A Complete Guide to Programming in C++ by Ulla Kirch-Prinz and Peter Prinz, I encounter a sentence:

Manipulators are functions that can be inserted into the input or output stream and thus be called.

Would anyone please explain me why it is "... and thus be called" but not "...and thus to be called"?

  • There's no "just" in that sentence at all. "Thus" is a completely different word. May 25, 2018 at 2:41
  • Many thanks Nathan. It is exactly the sentence from the book. By the way, would you please comment on what the grammar of "be called" is?
    – Ng.
    May 25, 2018 at 3:39
  • Which is the sentence from the book? You have three different quotes; one of them is the full sentence, with "thus", another is the trailing bit, but with "just", and the last is a hypothetical variant, also with "just". "Thus" is almost certainly the correct word here, and is also the first one used, so you should edit your question to make sure you're consistent, and asking about exactly what the book says. At present, at least part of your question is sure to be wrong. (You should also check the definition of "thus" to see if that clarifies things.) May 25, 2018 at 4:11
  • Do apologize for the mistakes in my question. The question has been corrected.
    – Ng.
    May 25, 2018 at 5:43
  • It's be called for the same reason it's be inserted and not "to be inserted". It's much easier to see if you simplify the sentence: "Manipulators...can be...called." You wouldn't say "Manipulators can to be called."
    – stangdon
    May 31, 2018 at 19:51

1 Answer 1


The auxiliary can takes a bare infinitive as a complement, not a to-infinitive:

I can read a book in one sitting.    (OK)
*I can to read a book in one sitting. (ungrammatical)

And you can see that in your example, too. Both clauses with be are complements of can, so in both cases we need bare infinitives:

Manipulators are functions that can [be inserted into the input or output stream] and [thus be called].

In other words, we can't insert to because can doesn't allow it.

The adverb thus is grammatically optional here and adds a meaning similar to 'as a result'.

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