Half doesn't or half don't?

Question

What’s the right version of these two?

1. Half of the students doesn’t bother to show up.

2. Half of the students don’t bother to show up.

Or are both right?

The related question Is two-thirds plural? discusses some relevant concepts, but the answer is very general, and it's not clear how to apply it here since "half" is a singular noun, while "two" is a plural noun.

Barrie England's answer there says that in "2/3 of the pizza was eaten," singular agreement is appropriate because "the emphasis is likely to be on the amount of pizza eaten, and not on the number of individual thirds. In contrast, in [2/3 of the visitors were men] the emphasis is on the number of visitors who were men, so plural concord ... is required."

What does it mean to put "emphasis" on "the amount" vs. "the number"? If "half of the students" is just an approximate or uncertain percentage (like "between 51% and 55%"), rather than an exact count, how do I know whether it's appropriate to emphasize the amount or the number of students?

Answer 1

You could make a logical case for either variant, but the only one that native speakers of English would say is

Half [of] the students don't bother to show up.

This is a case in which the outcome is dictated by synesis (see http://en.wikipedia.org/wiki/Synesis ).

Answer 2

English has a handful of premodifiers which, despite formally appearing to be a prepositional phrase, are not such for determination of the subject or for agreement with the verb. Other are a number of and a lot of, and in fact, half of the.

These premodifying phrases act as adjectives, and the grammatical subject remains the word following, which is either singular or plural, and thus so too much be the verb.

• A lot of the people are scared.
• A lot of the sky is blue.
• Half of the people are scared.
• Half of the sky is blue.

In other word, the premodifier does not affect grammatical number for subject–verb concordance.

Note that this is a special case, not the normal one. Therefore, other prepositional phrases would work differently, and indeed shift the subject and thus affect concordance:

• One of your best traits is your humor.
• Several of our membership have gone to their glory.

And sometimes you just cannot test, or require contextual clues.

• The best of us at our ring-tossing competition is made Mayor for the Day.
• The best of us at our ring-tossing competition are allowed to keep their rings.

Answer 3

I would have the tense follow the closest noun:

"Half of the students are sleeping."

as opposed to:

"Which half is going to pass?"