This question tests your understanding of subjunctive mood in English grammar, specifically after the verb "wish".

The verb "wish" is used to express a desire for a situation that is untrue, unreal, or imaginary in the present. When we use "wish" to talk about a present situation we desire to be different, we use the past subjunctive form. For the verb "to be", the past subjunctive form is "were" for all subjects (I, you, he, she, it, we, they).

Let's break down the sentence: "I wish he _____________ a little more tactful!"

The speaker is expressing a desire about a present situation. The reality is that "he is not tactful," and the speaker wishes this current reality were different.

Therefore, we must use the past subjunctive form of "to be", which is "were".

Analyzing the options:

• Might be: This suggests a possibility, not an unreal wish.
• Must be: This expresses certainty or obligation, not an unreal wish.
• Will be: This refers to a future certainty, not an unreal present wish.
• Would be: This is often used in conditional sentences for the future (e.g., "I wish he would be more tactful tomorrow"). For a present, unreal wish about a state of being, "were" is the grammatically correct choice.

Final Answer: The most suitable option is "were". The correct sentence is: "I wish he were a little more tactful!"

Related Topic: The Subjunctive Mood

The subjunctive mood is a verb form used to explore hypothetical or non-real situations, such as wishes, suggestions, demands, or statements of necessity. It often looks different from the standard indicative mood (used for facts).

Key Uses:

• After "wish": To express a desire for an unreal situation.
  • Present Unreal: I wish I were taller. (But I am not.)
  • Past Unreal: I wish I had studied harder. (But I did not.)
• After certain verbs (e.g., suggest, recommend, demand, insist, propose): She suggested that he leave early.
• After "it is important/necessary/vital that...": It is vital that she be informed immediately.

Key Formulae/Rules

Rule for "wish" + (that) clause:

• Wish for Present: Subject + wish + (that) + subject + past simple verb (for the verb 'to be', use 'were' for all persons).
• Wish for Past: Subject + wish + (that) + subject + past perfect verb (had + past participle).
• Wish for Future: Subject + wish + (that) + subject + would/could + base verb.