Even if you’re a great speller, automatic spell checking provides a valuable safety net, often preventing us from sharing with the world our own individual ignorances of the languages we communicate with.

For years, spell checkers of all kinds have relied upon word databases to determine that a word has been misspelled. I’m sure it’s at least a little bit more complicated than this, but in a nutshell: if the word you’ve just typed is not in this enormous list of words, then it’s probably a misspelling, and is marked as such.

Thus as you type your master works, when you either flub your typing or can’t recall the correct spelling, most modern editors will flag the word in question, for example by showing a red squiggle below it.

One challenge, though, is that for any individual, a number of words that are spelled correctly may nonetheless be absent from spell checker’s enormous database. One great example of this is the variety of proper names we deal in that may not happen to be included. For example, if I were a Boston Red Sox fan I might type Dustin Pedroia’s name often, and at least OS X’s built-in spell checker would mark it as incorrect. The workaround for these situations is to control-click the word and, from the popup menu, select “Learn Spelling” to avoid future flagging of the item.

The problem can be especially annoying when the OS repeatedly flags the names of people in your own family. For example, my own last name, “Jalkut,” is incredibly uncommon and would be flagged as a misspelling by most spell checkers in the world. However, on my Mac it is not, even though I’ve never asked the system to “learn” the spelling. In fact, none of the names of my family, friends, or business associates are marked as misspellings. How does this work?

Apple’s engineers realized that they could spare you the hassle of “learning” these spellings, since they already have access to a massive database of proper names that matter to you. Your Contacts database. If you’re on a Mac right now, open up the Terminal application and paste in the following line:

/System/Library/Services/AppleSpell.service/Contents/MacOS/findNames

The result that should come flying down the terminal window are the proper names of everybody and everything in your Contacts database. Specifically, Apple consults every entry in your database for the following attributes:

• First Name
• Middle Name
• Last Name
• Nickname
• Maiden Name
• Organization
• Address
• City

Each of these words, if present, is used to augment the already-massive list of correctly spelled words. So if you happen to know somebody named Frenk Xssl, who lives in Cwmystwyth and works for Infinitea, you can write all about them and their work, and never be bothered once by the tell-tale red squiggle of a word misspelled.