John's and Tom's sugar IS different or ARE different?

Question

When I say "John's sugar and Tom's sugar are different", I know it must be plural because there are two items in the subjective.

However, in "John's and Tom's sugar", there's only one item, so I should use "is"? But it's referring to two things, and telling people they are different, so it seems that "are" is more logical, right?

Or should I say "John's and Tom's sugars are different"? I know sugar is uncountable, but sometimes uncountable nouns also have plural forms, like "We'd like two coffees". But I'm not sure whether that's correct in formal writing.

Answer 1

The main issue is whether you are talking about an uncountable or a countable division of sugar between John and Tom. Uncountable nouns are singular:

Both John's and Tom's sugar is old.

Countable nouns are plural:

Both John's and Tom's sugars are old.

How do you decide which is right? Well, in this context, it makes more sense to assume you mean that John's sugar and Tom's sugar are of different varieties. Varieties of sugar are countable, so you would use the plural:

John's (turbinado) and Tom's (muscovado) sugars are old.

This could still be true even if talking about different defined quantities of sugar:

Both John's and Tom's bowls of sugar are old.

It might be a little confusing, but if it was obvious to the listener, you could leave out the exact measurement ("bowls of") and just say "sugars":

Both John's and Tom's sugars are old.

Lastly, just saying the sugars "are different" seems extraneous. Obviously they'd have to be, because the sugar belongs to different people. Instead you would say how they are different.

Both John's and Tom's sugars come from different countries.

Answer 2

If you say Tom's sugar and John's sugar, then you would want to use "are". But when saying Tom and John's sugar, you will have to use "is". To make it more undestandable, just ask this: "What is different?" -Tom and John's SUGAR is. To clearify, in the first one there are two groups: 1. Tom's sugar and 2.John's sugar, while the second one has only one group, which is Tom and John's sugar.