Quick shout out to Gina who mentioned this in the comments last week. It was on my list of things to discuss, so I moved it up because it is a very important thing for writers to be aware of. :)
WHO vs THAT
Which of the following sentences are correct?
- Roger is a serial killer that kills only bad people.
- Rapists, murderers, and drugs dealers are all people who deserve to die.
- The justice system is an outdated system who doesn't always work.
- Sometimes we need to resort to new measures that keep our streets safe.
When referring to a person, you have to use "who". The subject of sentence 1 is "Roger", and Roger is a person--not a "that", so the correct sentence would read, "Roger is a serial killer who kills only bad people". Likewise, in sentence 2, "rapists, murderers, and drug dealers" are people, so they also get the human treatment of "who".
Don't agree? Consider the following (I'm borrowing from Gina because it is a very good example): "I like girls who aren't obsessed with themselves." Would you argue that "girls" is actually an object? Well, I sure hope not!
Let's beat a dead horse, shall we? As long as it's one that doesn't stink up the place!
When referring to an object, use "that." In sentence 3, the subject is "justice system," which of course is an object. The correct sentence would read, "The justice system is an outdated system that doesn't always work." And in sentence 4, the subject is question is "measures," also an object.
You might notice I avoided using "pronouns" and "possessive" and all that technical jargon. Bleh. My job isn't to scare you off. In this instance, it's very easy to remember: human or non-human.
It might get fishy if we start talking about zombies though... Human? Non-human?
I cut off the head of the zombie that tried to eat my flesh.
I shot a hole in the head of the zombie who was chomping on my best friend.
I think in this case, it depends whether you or your protagonist is sympathetic towards zombies. Likewise, I'd probably refer to my dog as a "who" but refer to a random wildebeest as a "that."
It's all about context. And knowing the rules before you can break them. As Grammar Girl says here, you might talk about your evil step mother, "the woman that married my father" if you really don't like her, whereas you'd talk about your "sweet mother who divorced my father."
Agents won't immediately write you off for mistakes of this caliber, but if we see them constantly, in every paragraph, we start suspecting a lazy writer that didn't bother to learn their grammar manners (see what I did there?!).