I happened upon the following sentence in a textbook:

'An increase in the number and size of islets is characteristic of infants born to diabetic mothers.

I get that, as the sentence is presented, the singular noun 'increase' is governing the singular verb 'is', but aren't two different 'increases' being described, one in size and one in number?

On another note, I would probably see nothing wrong with 'The love of money and power was his undoing'. I'd imagine a single 'love' that embraces both 'money' and 'power'.

So, what's the rule in matters like this?


In this case it clearly is intended to mean that both number and size increase together, and therefore there's only one increase involved; and it is that joint increase that is characteristic.

It's not unambiguous; the author could mean that the number and the size vary independently. But that would be misleading, at least, since the verb is singular. And this certainly would be bad writing if that's what's intended. Better in that case would be separate NPs with a plural verb, and no conjunction reduction:

  • An increase in the number of islets and an increase in the size of islets are characteristic ...

Whenever material is deleted from a sentence (as repeated material is, in conjunction reduction), information is lost, and ambiguity becomes more likely. But mostly listeners don't notice it because of their expectations from the context. And this context is fairly straightforward.

Executive summary: It's more important for a writer to be clear than it is to avoid ambiguity.

  • +1 for a good answer but what do you mean by your executive summary? How can one be clear without avoiding ambiguity?
    – terdon
    Jul 19 '13 at 17:33
  • 1
    Being clear is mostly a matter of leading your addressee to the place where you want them, rather than making sure there are no other directions they can go. In this case the framing of the sentence with the two NPs conjoined, both subordinate to increase, which agrees with a singular verb, combine to lead the reader to the simplest reading. The fact that one can, by straining, get a different reading is not important, once that sentence is over and they're moving on to the next one. Ambiguity is a feature, not a bug. Jul 19 '13 at 17:49
  • And anyway, you can't avoid ambiguity, at least not in writing. Any written sentence is multiply ambiguous, as computational linguists have repeatedly discovered. Jul 19 '13 at 17:51
  • 1
    Fair enough, brings to mind the classic "Father: Doctor is it a boy or a girl? Doctor: Yes."
    – terdon
    Jul 19 '13 at 18:38

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