I have some doubts about the following issue. Let's say that we have a sentence:

It's difficult to perform the calculations.

Now, I want to make "the calculations" the subject of this sentence, so I write:

(1) The calculations are difficult to be preformed.

But is it correct not to use the passive voice? Something like that:

(2) The calculations are difficult to preform.

I thought that the passive is mandatory in such cases, but then I saw the following example from Cambridge Dictionary:

This meat is difficult to chew.

So, it isn't fully clear to me how to use it correctly. I would write something more like

This meat is difficult to be chewed.

Could anyone comment on that issue?

  • The meat is ready to be chewed. The doer (agent) experiences the difficulty. So we don't say difficult to be performed or difficult to be chewed.
    – TimR
    Nov 17, 2018 at 21:20

1 Answer 1


Clarifying the Meaning of a Passive Verb.

I perform calculations. Calculations are difficult to perform.

The calculations are performed by me. [passive]. The second sentence cannot be made into a passive. You need an action verb, not a adjectival phrase. "are difficult" cannot be made into a passive.

You need a subject + an action verb at the very least.

Active Sentence: He makes pies. Passive Sentence: The pies are made by him.

The computer performs calculations.

Calculations are performed by the computer.

You take the object and add "is" or "are" plus the past participle of the action verb then by plus the person or thing.

For example:

Active Sentence: They draw pictures.

"pictures" are the object. "are drawn" is the verb. "by them" is the agent.

Passive sentence: Pictures are drawn by them.

  • Thanks for the answer, but my main concern is about using phrase "difficult to". So following your example with the computer, the only right sentence is: "Calculations are difficult to perform by the computer"? Not "Calculations are difficult to be preformed by the computer? Because you see, without the phrase "difficult to" we would normally write "Calculations are performed by the computer". That is why I thought that the passive should also be in the sentence containing "difficult to".
    – Arci
    Nov 17, 2018 at 21:56
  • 1
    @Arci Ok, allow me to be straightforward. You have not yet grasped what a passive verb is in fact. There is no passive in any of your examples and they are incorrect. "are difficult, are easy, are + any adjective" is not an action verb. It is the verb to be plus an adjective. That cannot be made into a passive. "The calculations are difficult to perform." not: to be performed. The tasks to be performed are difficult. No passive there either.
    – Lambie
    Nov 17, 2018 at 22:01

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