The subject of the verb is an invention - which is singular, so the verb-form should be too.

Here are a few written instances of "are an invention that has". Note that Google Books contains no examples of "are an invention that have".

Don't bother even thinking about what Microsoft Word recommends or queries - at best it might be useful for flagging up glaring typos/etc. Beyond that, it has no credibility.

I would say that "has" is correct, and doesn't need to be replaced with "have". That's not to say that "have" is necessarily incorrect. Some people might prefer "have" because it is somewhat awkward to apply the concept of "not having heard" of something to a group rather than to its individual members.

I think that my answer to a deleted question about the sentence “I find it good that 50% of the American population (are or is) cool” is relevant, so I have re-posted it below:"

Singular agreement seems to be more common with "X% of the population"

The Google Ngram Viewer seems to indicate that both agreement patterns are in use, but that "...percent of the population is" is notably more common than "...percent of the population are" (and to a lesser degree, "...cent of the population is..." is more common than "...cent of the population are..."):

Also, "is" sounds more natural to me in this case. (I can imagine dividing the population into two parts, and saying "this part of the population is cool; that part of the population is uncool." So it seems clear that "is cool" can sometimes be used as a predicate after an expression referring to a group of people, and this seems to me like a situation where it would be appropriate.)

But unsurprisingly, it seems that not everybody shares my opinion on that: Jim left a comment saying

I seem to prefer ’are’. When thinking about it I removed ‘of the American population’ and it seems like with ’are’ the statement is about the people behind the number, and with ’is’ the statement is about the figure (50%) itself.

I would generally recommend singular agreement, especially in a case like this where the verb is just the copula and the predicate is an adjective like "cool" that doesn't imply any particular grammatical number.

I don't think the type of predicate makes a big difference

I would hesitate more with predicates that contain noun phrases that seem to imply a particualar grammatical number, like "drives a red car"/"drives red cars". Actually, predicates that contain noun phrases often pose tricky questions about grammatical number in general: e.g. the problem of whether to say things like "they all nodded their head" or "they all nodded their heads", where some people think the first sounds like they all share one collective head and other people think the second sounds like they each have multiple heads.

I tend to be in favor of using plural noun phrases in this kind of context, but I don't think that means that the verb has to be plural. I actually think I would be in favor of using a singular verb and a plural noun phrase in most cases, like "XX% of the population drives red cars". I can see why somebody might feel like that sounds odd, but there is no rule that requires a verb to have the same grammatical number as any noun phrases contained in the verb phrase (see Agreement in "[Singular Noun] Is/Are [Plural Noun]"?).

Since my preferences are already in favor of singular verb agreement by default, I didn't think at first about situations where notional agreement principles would cause singular agreement to be more likely than usual. But I think there are some circumstances where this is the case: a sentence like "50% of the American population is a large amount of people" seems to require singular verb agreement.

Also, singular verb agreement seems necessary in at least some circumstances, but not all, for an author who does choose to use a singular noun phrase in the predicate. While "XX% of the population drive a red car" sounds kind of OK to me (and similar sentences are attested in the wild, like "56 percent of Americans have a profile on a social networking site"), something like "XX% of the population are a felon" sounds completely wrong to me: I would say it has to be "XX% of the population are felons", "XX% of the population is felons" or "XX% of the population is a felon" (my preference is for one of the first two because the last seems illogical to me, but constructions like "XX% of Y is a Z" do seem to have some use, and aren't anywhere near as jarring to my ear as "XX% of Y are a Z").

Example quotes:

• About 32 out of every 1000 people is a twin. (the twin project @ the university of texas)

  (notes: while "people" is unambiguously a plural count noun in this context, it is an irregular plural, which may facilate the use of this agreement pattern. I wouldn't recommend it, just wanted to show it is out there)

• the remaining portions of the population are a mix of Serbs, Hungarians, and Gypsies. ("A Deeper Understanding of Croatia’s Culture", by MARILYN VILLANUEVA)

  (notes: this was one of the only examples I could find of the sequence "of the population are a", and note that the following phrase, despite starting with the indefinite singular article "a", is really plural in signification: "a mix of [plural nouns]")

Links and quotations

I found some discussion of the matter on other sites; here are some quotations that I thought were relevant (still being updated):

Here is also what Martin Hewings says, in English Grammar in Use, unit 52, about that point.

After per cent (also percent or %) we use a singular verb:

"¢ An inflation rate of only 2 per cent makes a big difference to exports.

"¢ Around 10 per cent of the forest is destroyed each year.

However, in phrases where we can use of + plural noun we use a plural verb:

"¢ I would say that about 50 per cent of the houses need major repairs.

"¢ Of those interviewed, only 20 per cent (= of people interviewed) admit to smoking.

But where we use a singular noun that can be thought of either as a whole unit or a collection of individuals, we can use a singular or plural verb (see also Unit 51B):

"¢ Some 80 per cent of the electorate is expected to vote, (or ...are expected...)

(Grammar Q & A Newsgroup, "2 percent is/are?", posted October 01, 2008 10:39 AM by Izzy loves you all)

There is also a document about subject-verb agreement from the old "Yale Graduate School Writing Center" floating around (I couldn't find it on their current site) that gives

21% of the population is poor

as an example of the rule

When an –of phrase follows a percentage, distance, fraction, or amount, the verb agrees with the noun closest to the verb.

I wouldn't rely on either of these, but I think they support the idea that singular agreement is acceptable (and the first supports the idea that plural agreement is acceptable).

Other relevant questions:

• Why is a singular verb "is" used after "One-third of the population" while a plural verb "live" is used after "70 percent of the population"?

• the world('s) population speak/speaks

As you may know, have and has are both present forms of the verb to have and are employed with the verb have alone (for a present simple), with have/has (used as an auxiliary verb) and the past participle of another verb (for a present perfect) or with have/has (used as an auxiliary verb), the past participle of be and the past participle of another verb (for a present perfect continuous).

• Has is used with a third singular person ("he", "she", "it", or a noun) i.e. when the subject is singular but it's neither the person who's writing/speaking ("I") or the person who's reading/listening ("you"):

  • He has just asked a question.

• Have is used in any other case:

  • Can anyone tell me when we have to use "have", etc.

  • I have just copied a sentence from your question.

  • Have you noticed it?

Here you will find the complete conjugation of the verb.