When we wasn’t trying to keep up with John McCain’s references to Joe the Plumber, Barack Obama made a number of linguistic errors tonight.

“If you make less than a quarter million dollars a year,” he said, your taxes will not be increased. Later he noted that 98 percent of small businesses “make less than $250,000.”

When describing something you can count individually, like income, use fewer. If it can’t be counted, use less. Obama vowed that Americans who earn fewer than $250,000 will not experience tax hikes.

Obama also tripped on who vs. that. In defending his running mate, he said, “Joe Biden is, I think, one of the finest public servants that has served in the country.” When describing people or named animals, use who. Biden is one of the finest servants who served the country. (Or, better yet, led or lived in the country.) That is reserved for unnamed animals and objects — not running mates you’re trying to praise.

The smiling senator made a few poor word choices tonight. For example, he tried to deny McCain’s claim that an American earning $42,000 could experience a tax hike. That notion has been “disputed,” Obama said. “Even Fox News disputes it, and that doesn’t happen very often when it comes to accusations about me.”

To dispute means to discuss or debate. It may call the veracity of a statement into question, in its most forceful applications, but it is not a synonym for deny, to state that something is untrue, which is what Obama was going for.

There is a continuum of disagreement that begins with dispute and ends with rebut:

• dispute: to debate

• deny: to state that something is untrue

• refute: to provide evidence to the contrary

• rebut: to successfully prove wrong

We’re here to dispute politicians’ language tonight so that you can rebut your boss’ email tomorrow.