Learn the rule (or how to avoid the issue).
When in Doubt, Rewrite
To avoid the “whoever/whomever” problem altogether, you could rephrase it as as “the person who” or “the person whom,” or even just “the person.” So instead of “I want to speak to whoever did this,” you’d have “I want to speak to the person who did this.” Instead of “Whomever I hire will start immediately,” you could write “The person I hire will start immediately.” When you’re faced with a “whoever/whomever” choice, it’s often a good time to dodge the issue and simplify your sentence.
This article was written by Neal Whitman, who has a PhD in linguistics and blogs at Literal Minded, and it was edited and read in the podcast by Mignon Fogarty, author of Grammar Girl’s Quick and Dirty Tips for Better Writing.
1. Zwicky, Arnold. June 18, 2007. “ISOC, ESOC.” Language Log post, http://itre.cis.upenn.edu/~myl/languagelog/archives/004616.html (accessed June 9, 2011).