grammatical number - "Was" or "were" for "half a dozen"

In Microsoft Word, the following sentence is flagged. It tells me to use "was" instead of "were"

There were half a dozen books strewn about the floor.

I would think that you would use "were" since it's a quantity more than one. You wouldn't say, "There was twelve books strewn about the floor." Does the use of the "half" modify it somehow?

Answer

Formally speaking, the Word grammar checker is right. The subject of there were is the word half, which is singular. So under formal grammar the sentence should be:

There was half a dozen books on the floor.

However, many people find this sentence to be odd in practice, since English speakers often prefer "semantic number agreement", in which the effective plurality of a phrase is determined by its meaning and not the grammatical number of its head. Therefore, for many registers people prefer your original example:

There were half a dozen books on the floor.

If you're writing something formal and can't abide to say there was half a dozen, then rephrase the sentence to avoid phrases like half a dozen.