Here's why:
* Subjunctive mood: The subjunctive mood is used to express a wish, a hypothetical situation, or a suggestion.
* Past tense: The past subjunctive is used to refer to a past action or state in a hypothetical or conditional context.
* Plural: "Were" is the plural form of the past subjunctive of "be".
Example:
* "I wish they were here to celebrate with us." (Expressing a wish in the past subjunctive)
Let me know if you have any other questions!