Here’s a neat fact I learned from Geoff Pullum’s radio talk about singular ‘they’.
It’s appropriate to use ‘they’ in spoken English as a singular pronoun, provided it plays something like the role of bound variable. So (1) could mean (2)
(1) Every scientist said they believe in evolution.
(2) [All x: scientist x]Believe in evolution(x)
The proviso is important. You can’t use ‘they’ as short for ‘he or she’ (as it appears to be used in (1)) when it is anaphoric on a name.
(3) Morgan said they believe in evolution.
In (3) ‘they’ has to refer to some group. Morgan might be a part of that group, but he or she can’t be denoting him or herself with ‘they’. Wouldn’t it be easier if I could say there “they might be denoting themselves”? I can’t, which shows that the use of ‘they’ here derided by some self-ordained grammarians is actually rule-governed. (If anyone has seen Bill Safire sounding off on this use of ‘they’ I would be very happy to see quotes!)
It’s not just universal quantifiers that can bind singular ‘they’, as the following examples show. (These are all from Pullum.)
‘Everybody should marry as soon as they can do it to advantage.’ That’s Jane Austen in 1814. And there are thousands of other examples down the years.
‘A person can’t help their birth.’ (That’s William Makepeace Thackeray in 1848.)
‘Nobody fancies for a moment that they are reading anything beyond the pale.’ (That’s Walter Bagehot in his book ‘Literary Studies’ in 1877.)
‘… at the end of the season when everyone has practically said whatever they had to say …’ (That’s Lady Bracknell speaking in Oscar Wilde’s play, The Importance of being Earnest in 1895, and Lady Bracknell never says anything ungrammatical.)
‘Who ever thought of sparing their grandmother worry?’ (That’s Edith Wharton writing in 1920, using singular ‘they’ with ‘who’ as the antecedent).
‘Too hideous for anyone in their right mind to buy.’
The conclusion Pullum draws from this data is:
The relevance of the distinction is this: in English, the pronoun ‘they’ is fairly strictly limited to having a plural-inflected antecedent when it is used as a referring pronoun, but there is no such restriction when it’s a bound pronoun.
He attributes much of this to a PhD dissertation by Rachel Lagunoff, who pointed out that some genuinely existential quantifiers can govern ‘they’ as in (4)
(4) There’s a caller with a musical question on Line 1. They realise they may have to wait. (This was an example Pullum noticed while going in to the studio to record the talk I’m ripping off here.)
I’m not sure referential/bound is quite the right distinction here, because I think (5) sounds bad, even if the definite description is uncontroversially attributive.
(5) The scientist said they believe in evolution.
Still, I think there’s a good point that when the NP is referential, singular ‘they’ is inappropriate. Which brings me back to the title. Some of the time I can convince myself that complex demonstratives can licence singular ‘they’, as in (6).
(6) That scientist said they believe in evolution.
(6) is a little marginal, especially compared to the Austen to Auden examples above, but I think it can be OK. And that’s a bit of evidence (hardly compelling, but evidence) for the claim that complex demonstratives are quantificational rather than referential.
Confession. I haven’t gone and looked up the literature on complex demonstratives, and for all I know this argument has been refuted more times than I’ve had Chinese dinners. If not, I gladly offer up some more evidence for the quantificational side of the disputes about complex demonstratives.