On the other hand, paper-based books are more difficult to be stored \ to store than electronic books.

A research using Google Ngram shows that the passive form "difficult to be stored" is never used but I cannot understand the rule here. Could you please help me to analyse this?

  • Neither of these is the passive.
    – Peter Flom
    Commented Aug 9, 2019 at 11:49
  • @PeterFlom I think it is wrong structure but why "be stored" is not passive? or how it is wrong?
    – Costa
    Commented Aug 9, 2019 at 11:51
  • 3
    "Paper-based books are more difficult to store than electronic books" is intransitive; there is no direct object, so it can't be passivized..
    – BillJ
    Commented Aug 9, 2019 at 12:46
  • 2
    Because the adjective "difficult" resists having a passive clause as its complement. The result is unnatural, as you can see.
    – BillJ
    Commented Aug 9, 2019 at 14:50
  • 1
    – athlonusm
    Commented Dec 18, 2019 at 11:03

2 Answers 2


Consider the sentences

1) Storing paper-based books is more difficult than (storing) electronic books. 2) To store paper-based books is more difficult...

In this case "storing" or "to store" is a gerund - A verb form (the present participle or infinitive) used as a noun, in this case, the subject of the sentence. But since storing is being used as a noun, you can't make it passive.

I'm not sure this is an answer, but it is a least an analysis.


As BillJ says in a comment, difficult resists taking a passive infinitive complement.

But I think this is primarily a semantic restriction. When you use difficult to X, the presumption is that the subject of X is the entity who experiences difficulty:

I find it difficult to walk slowly.

So if you used a passive:

Paper-based books are difficult to be stored

it means that the books are finding it difficult, not that you are.

With suitable verbs and context, you can use a passive infinitive:

It is difficult to be heard, with all this noise around.

I don't think this is very common - most people would say something different, such as It is difficult to make yourself heard; but it is possible.

You can, of course, also say

It is difficult to hear, with all this noise around.

but that is from the perspective of the hearer, rather than the speaker.

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