The sentence "I wish I could speak to him" is an example of a sentence using the subjunctive mood, specifically a wish clause.
In this sentence:
"I wish" is the main clause, expressing a desire or regret.
"I could speak to him" is the subordinate clause, expressing the desired or regretted action.
The verb "could" is in the past subjunctive form, used to express a hypothetical or uncertain situation. This is a polite or formal way to express a desire or regret.
