If I had to chart the times writers have asked about the differences between these two words, it’d be, well, off the chart.
“Indices” is the plural of index, which makes it a noun. For example: “The politician presented several economic indices to prove we’re still in a recession.”
“Indexes” is the present tense of the verb “index.” To wit, “Jane indexes her DVDs alphabetically.”
This all may be changing, though. The Wall Street Journal’s stylebook says using “indexes” as a plural of “index” is acceptable, and many spell checks will tell you that “indices” is wrong.
Over time, we’ll probably see usage of “indices” fall to an all-time low.
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My name is Rob Bignell. I’m an affordable, professional editor who runs Inventing Reality Editing Service, which meets the manuscript needs of writers both new and published. I also offer a variety of self-publishing services. During the past decade, I’ve helped more than 300 novelists and nonfiction authors obtain their publishing dreams at reasonable prices. I’m also the author of the 7 Minutes a Day… writing guidebooks, four nonfiction hiking guidebook series, and the literary novel Windmill. Several of my short stories in the literary and science fiction genres also have been published.