As William Zinsser says, "Bad writing makes bright people look dumb."

Some errors are painful, such as the wrong verb form in "I could have did better." Some errors are inconsequential, such as the missing hyphen in the compound adjective in "a record setting pace." And some errors are distracting, such as the incorrect subject-verb agreement in "The problem with computers are their lack of dependability" and the unnecessary comma between the subject and the verb in "The temperature at the start of the Seeley Classic cross-country ski race, was four degrees."

But learning the rules is only half the problem. We also must know when the rules change. The correct use of who versus whom is an example.

The old rule was straightforward: Use who when the pronoun is a subject, as in "Who wrote this nonsense?"; use whom when the pronoun is an object, as in "To whom should I send this nonsense?"

See if you can choose the correct usage in the following sentences:

1. "Who/whom did this?"

2. "Who/whom should I turn to?"

3. "The person who/whom wrote this report did an excellent job."

4. "I don’t know who/whom to trust."

5. "I know who/whom is responsible for this mess."

In the first sentence who is the subject. In the second sentence whom is the object of the preposition to. (In formal or traditional usage, that sentence would be reordered: "To whom should I turn?") In the third sentence, who is the subject of the subordinate clause "who wrote this report." (The main clause is "The person . . . did an excellent job.") In the fourth sentence whom is the object of the infinitive to trust.

The fifth sentence is tricky. At first you might think whom is the object of the verb know, but look closely. Who serves as the subject of the subordinate clause "who is responsible for this mess." In sentences like this one, pronoun case (the subjective case who or the objective case whom) is determined by how the pronoun functions in its own clause.

Got that?

So, should it be who or whom in the following sentences?

1. "I wasn’t sure who/whom to vote for."

2. "She knew who/whom would do a better job.

3. "Tell me who/whom won the race."

If you chose, whom, who, and who, you know the rule. Now for the challenging part. (Did you think we were already there?)

The rule is changing. Perhaps because whom sounds formal and stilted to the modern ear, it is becoming less common. Who is becoming acceptable where whom was called for by traditional grammar, as in "Who can I turn to?"