'What reading does is encourage comprehension and our ability to focus.'

As far as I'm concerned there's nothing wrong with this sentence. However, I'm aware that one could add 'to' before encourage. I would like to know whether any prescriptivists would say it should include 'to' or whether as a matter of style in formal English it would be better.

Thanks for any ideas on this.

  • Possible duplicate of Is it correct to use question words in declarative sentences? (where John Lawler says that the to is optional after a what-cleft): 'I want him to trim the hedge. =Wh-Cleft=> What I want him to do is (to) trim the hedge. There's probably a closer duplicate to the question wording. Aug 11 '19 at 14:40
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    Aha. Is this sentence correct? 'What I want to do is read this book' (J Lawler answers). Aug 11 '19 at 14:48
  • In the example I've cited as a dup, things are complicated by the fact that the example under consideration (What I want to do is [to] read this book) includes both want and do within the context preceding the (optionally "unmarked") infinitive verb. That's what makes the second [do] "optional" in that specific example. If we have just one verb or the other (What I do is read this book, What I want is to read this book) there's no choice - do requires an "unmarked" infinitive, but with want the marker to must be present. Aug 11 '19 at 15:02
  • @EdwinAshworth: Maybe I missed something, but I don't see anything in John Lawler's answers to either of the earlier questions addressing the specific matter of "unmarked infinitives" - as opposed to simply "deleting" the second occurrence of to in What I want to do is [marked / unmarked infinitive]. Aug 11 '19 at 15:07
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    Where the subject noun phrase includes "do" in a relative clause, as it does in your example, "to" can be added. I'd say it is a free choice.
    – BillJ
    Aug 11 '19 at 15:28

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