Some call it subjunctivitis: the problem created by those "I wish it were" and "if he were" sentences. They sound odd because of an apparent subject-verb disagreement. But that's subjunctive mood for you.

According to the Columbia Guide to Standard American English, mood "suggests part of the speaker's attitude toward the action the verb specifies." Here are some moods the guide mentions:

• Indicative indicates a statement of fact: "Austin is the capital of Texas." Questions that ask for facts are also indicative.
  
• Imperative indicates a command: "Get out of here!"
• Subjunctive indicates a "what if" tone of conjecture or possibility: "If I were president, there would be a chicken in every pot."

Sometimes people try too hard to be correct and use the subjunctive when they don't need to. This happened in a recent NPR report on Mel Gibson's brush with the law. "Gibson asked the officer if he were Jewish," the reporter said. Gibson was looking for a statement of fact, not conjecture. Here's a better way to express that idea: "Gibson asked the officer whether he was Jewish."

For more on the subjunctive mood, take a look at this column by James Kilpatrick.