relative clauses - "one of the upgrades that is/are being considered"

I've run into this problem multiple times when writing the following:

1. "one of the upgrades that is being considered is a ..."

Word spell check suggests that this is incorrect and it should be:

2. "one of the upgrades that are being considered is a ..."

This correction seems wrong to me as "one of the upgrades" is essentially a singular noun; I am referring to one upgrade.

Thanks for any help on this!

Answer

I see two cases:

• There are many possible upgrades. One that is being considered is . . . .



• There are many possible upgrades that are being considered. One of these is . . .

When the "that" refers to "one", the singular form "is" agrees with its subject.  When the "that" refers to "upgrades", the plural form "are" agrees with its subject.

If it remains your intention that the clause "that is being considered" modify the pronoun "one", you have chosen the correct form of the verb.

It is as valid for this clause to modify the object of the preposition, in which case the plural form of the verb would be required.  Without further context, determining the better of these two choices is not possible.

"One of the upgrades that is being considered" implies that there is some number of upgrades that are not being considered.  "One of the upgrades that are being considered" does not imply anything about upgrades that are not being considered.  You may wish to base your choice on whether the implication of unconsidered upgrades is something that you wish to include.

 
Word, of course, is unaware of this implication.  It simply notes that the clause as it stands does not agree with its closest possible antecedent.