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Given two sentences with the same subject, we can merge them into one.

The rooftop designs differ in their ability to keep buildings cool. The rooftop designs differ in their ability to capture rainwater.

The rooftop designs differ in their ability to keep buildings cool and differ in their ability to capture rainwater.

However, part of the predicate is also similar, so you can simplify further. However, it is uncertain to me how to handle the grammatical number of the word ‘ability’ after the simplification, keeping in mind we want it to remain clear that there are two distinct abilities & not two manifestations emerging from the difference of a single trait or ability.

I feel that omitting all of the repeated predicate splits the second infinitive & conflicts with the general intention, in the sense that it sounds like a single, albeit complex, ability.

The rooftop designs differ in their ability to keep buildings cool and capture rainwater.

Alternatively, including the ‘to’ makes mention of both abilities, but refers to them as a singular.

The rooftop designs differ in their ability to keep buildings cool and to capture rainwater.

There is, I think, an argument to be made in favour of the latter. Namely, one could argue that there is a tacit “[in] their ability” before the second infinitive, & thusly both remain singular.

The rooftop designs differ in their ability to keep buildings cool and [in their ability] to capture rainwater.

I am, however, still unsure how to go about this phrase. And, in a more general sense, I was wondering if there is a rule of thumb or something to be more confident hence.

  • I my view, the best is the shortest. The rooftop designs differ in their ability to keep buildings cool and capture rainwater works fine. I would suggest you use capacity instead of ability, though. – ralph.m Dec 11 '18 at 4:14
  • @ralph.m The preposition mostly needs to be repeated. Read the compound sentence without the second to and notice that it means something different altogether. – Kris Dec 11 '18 at 7:56
  • This question is better asked on Writing. – Kris Dec 11 '18 at 7:56
  • @ralph.m thankyou for your suggestion. Actually the sentence is originally from a textbook, in which they used ‘to’ in both instances. The textbook might have chosen ‘ability’ because I think it’s a more common word. – Shiro Rorek Dec 11 '18 at 9:04
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    @Kris I also like the version with explicit prepositions, but I don’t know about “mostly needs”. In clause lists it is common to omit them (if they’re all the same). This site suggests you don’t say “I am cooking a stew with beef, with carrots, and with onions”; with which I agree. Also, thanks for the idea; I have never visited the Writing Stack, I will see if other people think the same. – Shiro Rorek Dec 11 '18 at 9:08

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