Yes, I have an agenda. Note particularly that I said an agenda, with the word ‘an’ heavily emphasised. Yes, that’s right; I used agenda as a singular noun! Now, where are all the Latin experts reeling in horror, falling off their perches and writing self-righteous letters declaring that agenda is the plural of agendum?  There is not one to be seen. And we even use agendas for the plural, though agendae appeals to me as a cheeky but incorrect alternative.
Agendum has faded from the language. Is it because our increasingly duplicitous nature these days means that nobody is ever plotting just one thing? Maybe it’s because it looks bad if the to-do list for a meeting only takes up one line on an otherwise blank page. Who knows? Who cares? Me, for one: the title of this piece really should have been ‘I have an agendum’, since I’ll only be grizzling about one thing, but then the rhetorical flourish in the first paragraph would have withered. 
For you see it’s not ‘agenda’ that’s on my agenda, but rather it’s ‘data’: why are people so determined to use ‘data are’? Should a ‘data is’ appear, the aforesaid Latin experts descend like banshees en masse. They can’t accept that data has attained the meaning of a collective noun—a synonym for information, and shorter to boot. True, we have a slight paradox in that data (collective noun) is not only made up of lots of data (plural of datum) but can also be made up of lots of data (collective noun). It doesn’t matter how much extra data you add to your data, you still just have data. Data is like a black hole absorbing everything.
Mind you, unlike agendum, datum hasn’t died and indeed thrives, particularly in the geodetic datum of surveying: here, a datum is a set of reference points relative to which other points on the Earth are measured. So there we have it: even datum itself has achieved a sort of collective status. What’s more, it has its own plural, the sensible datums, to take into account all the failed attempts to make the perfect geodetic datum. There’s hope for the ‘data is’ believers yet.
Meanings change and new words enter English all the time. The use of trial as a verb—replacing perfectly good words like test or evaluate—took less than a year to sweep through the language.  Yet poor old data labours on, coupled with the inevitable ‘are’, long after its meaning evolved. Perhaps data is available somewhere to show why the use of ‘are’ has such a great following.  
I implore you to chastise the media whenever a ‘data are’ is found because the media are responsible for perpetuating the problem. No, wait; shouldn’t that be ‘the media is responsible …’? No, I don’t mean that literally—the media can be totally irresponsible at times—but have we decided that media is indeed a collective noun, like flock for sheep? 
It’s up to you to do your bit: replace ‘data are’ with ‘data is’ whenever you see it. And, if people insist on replacing ‘data is’ in your writing with ‘data are’, do as I do to spite them: replace their replacement with ‘information is’.
- This is a rhetorical question! They are all waiting to pounce on the problem in paragraph three.
- The editor of CRANK has hinted that you should split your gripe agenda up into individual agendums to increase the number of submissions—why write one article when you could write two! [Editor's note: or even three]
- Surprisingly ‘try’ as in what is done to the accused hasn’t been replaced by ‘trial’ … yet.
- The is-ites might be winning: Google search results for “data is” 46.6 million vs “data are” 22.9 million.
- Excessive meaningless footnotes interrupt concentration, a gripe I shall leave for another time.
- Gems can be found on the internet: the media are expected to show up and hold a séance.