But what about a sentence like this:
The Catskills is/ are the New York City watershed?
I am currently reviewing an otherwise excellent book (Life in the Himalaya) in which the author, M. Pandit, insists on using the singular Himalaya throughout the book. He bases this on the Hindi etymology of the name (discussed on p. 3), but that strikes me as nonsense. In the review I use the plural, but without otherwise making an issue of it. Different (key) strokes for different folks, I suppose, but if I were writing in Hindi (of which there is 0 chance) I would feel obliged to follow Hindi's grammatical rules, not English's.
Welcome to the Grammar Exchange, Mr Seymour, and thank you for your question.
The Ultimate Source Of All Knowledge (which is how I often jokingly refer to Wikipedia) appears to support the use of "Himalaya" as an acceptable alternative to "Himalayas" in English, but unfortunately, the main article doesn't cite sources to support this use. I found the dialog on the "talk" page much more helpful:
I've always been familiar with the terms "Himalayas" or "Himalayan Mountains", which I believe is the preferred way to refer to them in the United States.
We have some limitations here at GE. I'm guessing from his name that Mr Pandit is a highly educated Indian, who is very fluent in English as a second language that he has known almost since birth. I may be wrong about that, but I'm not going to take the time to fact-check him. My point is that we at GE have limited resources and mostly have to focus on English as spoken in the United States. To that extent, I have to agree with you. You should refer to the Himalayas as you are used to calling them, except in direct quotes, when you should adhere to Mr Pandit's choices. Because I am not an expert in how English is spoken abroad, though, I can't say that Mr Pandit is wrong. English is widely spoken in India, and it may be that "Himalaya" is preferred among English-speaking people there. But that doesn't make you wrong, either. It's regional. And, apparently, it is considered both singular and plural among them, as "deer" and "fish" are among us.
By the way, I would never pluralize any mountain range that begins with "sierra", which means "mountain range". To speak of the "Sierra Nevadas" is to speak of the Snowies Mountain Range. I would always leave the final "s" off.
But what about you? You are "reviewing" Mr Pandit's book. Are you doing this as a journalist, or as a scholar? It's none of our business, really, unless you choose to make it so, but it's a point of interest.
I hope this was helpful.
Further on "Himalaya(s)":
I suspect that English is Pandit's main language. Anyway, the book is published by Harvard University Press, so it should be written in American English, and indeed is--except for "Himalaya." Probably the editor and author battled it out over this one, and the author won, which in a way (I'm usually author!) I like.
Here is what he writes on p. 3, with my comments in square brackets [ ]:
"Let me begin by pointing out the use of Himalaya in singular form throughout the book as opposed to the pluralised version widely [almost universally] used in literature. The latter is, put simply, a colonial legacy. [Well, so is the use of English at all, the language in which he is writing. That is no excuse for getting it wrong. He is free to write in some other language; instead he chose to write in the language of his fellow former English colonists, the Americans.] Himalaya is a Sanskrit name (Him = snow, Alaya = home). Like the Alps and the Andes, the Himalaya cannot be pluralized. [Non sequitur. They can't be pluralised because they, like Rockies, Adirondacks, etc etc. (except for some names derived from Spanish, though often not even then, n.b: Pyrenees) are already plural. They always take plural verb, whereas he always uses singular verbs after "Himalaya."] ... I Have generally used the term Himalaya to mean the entire mountain range.... [This begs the question of whether he is taking about the general area (in which case the singular might be appropriate but should not be over-done) and the actual mountains, which is usually what he means so it should be plural. He doesn't seem to get this distinction.]"