Why has the author used "that" in the sentence below? I think "those" is correct here. Please help me to understand it if I am wrong.
. . . takes decisions and takes actions that promote the efficiency and effectiveness of its own department and that of other departments.
It's ambiguous if it should be that or those.
The noun phrase is efficiency and effectiveness. But the phrase can can be treated as either a single compound concept (leading to the singular pronoun that) or the conjunction of two distinct things (leading to the plural pronoun those).
In other words:
1) . . . the efficiency and effectiveness of its own department and that of other departments.
2) . . . the efficiency and effectiveness of its own department and those of other departments.
This is no different than drinking and driving or fish and chips.
For example:
The thing I don't like is drinking and driving.
The things I don't like are drinking and driving.
Neither interpretation is necessarily right or wrong. It depends entirely on how each person interprets the phrase—as a singular compound or a conjoined plural.
. . . takes decisions and takes actions that promote the efficiency and effectiveness of its own department and that /
thoseof other departments.
It can only be singular "that".
In their independent use, demonstratives function as 'fused' determiner-head in NP structure. Thus "that" is interpreted as "that efficiency and effectiveness".
"That" is appropriate here because "efficiency" and "effectiveness" are so closely related as to be interpreted as a single concept; "those" is inappropriate because it would leave people puzzling over what precisely was the distinction intended between the two.
That is a fused determiner head in the example given. When it comes to coordination of nouns, demonstratives this and that agree with the head. For example:
* Those cup and saucer.
The heads here are singular cup and saucer so the demonstrative would have to be singular this.
This explains why singular that is used and not plural those, which is clearly ungrammatical if the heads are added back in:
* those efficiency and effectiveness of other departments
That is put to good use here as it takes the place of the which is not allowed as a fused determiner head.
* ...promote the efficiency and effectiveness of its own department and the of other departments
For this to work, as the other answers have mentioned, there must be a close association between the two coordinates allowing us to think of them as a unit. This condition is satisfied by efficiency and effectiveness as one would seem to promote the other.
Unless the speaker and hearer have a shared singular conception of "efficiency and effectiveness", like as a company policy, then this is going to sound wrong to most readers, or at least those readers that stop and think about it. So it should be "those", because there are two objects being promoted, which are typically deemed to be separate.
Although who knows what the author intended, it seems like they either (a) made an antecedent error; or (b) are trying to make "efficiency and effectiveness" into a unified noun phrase, which really only works if your potential listeners share that concept.
An antecedent processing error. This is a common enough error even among native speakers, who often use the heuristic of looking to the last word referred to ("effectiveness") and inserting the corresponding pronoun form.
So as written the sentence "sounds" right on a very quick read (or writing) because one's mind does a kind of lookback function, like "was the last thing I said a plural noun or singular? ok, singular, let's say 'that' instead of 'those'".
In about 99% of sentences that heuristic works. Here it fails, and one has to really read the sentence slowly and be like "ok, these are two things that, grammatically, have to be put together to act as a plural, and so I use the plural pronoun to refer to them". That would be my suspicion as to what happened here.
Treatment as a singular noun phrase requires shared understanding of its singularity. There is, as Jason Blassford states, the possibility that the author intended for "efficiency and effectiveness" to be a singular noun phrase, like "fish and chips" or "drinking and driving". However, the difference is that "efficiency and effectiveness" do not exist most people's lexicon as a unified concept.
So while I, like most readers, would recognize either "pass me that fish and chips" (referring to the whole basket of food a single item) or "pass me those fish and chips" (referring to them is a collection of items) as grammatically valid, that is only because writer and reader share an understanding of them as a pair that can be unified.
"The thing I don't like is drinking and driving" and "The things I don't like are drinking and driving" are two sentences with two different meanings: the writer of the former is probably ok with you day-drinking at home in quarantine; but the writer of the latter probably isn't. The salient thing here is that the former only sounds grammatical because there is a widespread understanding of "drinking and driving" as a unified concept.
If one were to say, for example, "The thing I don't like is efficiency and effectiveness," in most contexts the listener is going to be like "Uh, wait, what? Which thing don't you like? Efficiency? Or effectiveness?" That sort of phrase would only work if the speaker and listener shared a unified concept of "efficiency and effectiveness", like if that were the name of a policy at a company where they both work.
