You don't ever have to double click to launch an application or open a folder if its icon is in the Dock.
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On your OS X Mac, here's how to make a single click perform double duty

April 9, 2006

By Al Fasoldt
Copyright © 2006, Al Fasoldt
Copyright © 2006, The Post-Standard

   Anyone using Windows XP can turn on a special mode that eliminates the need to double click to launch a program or open a folder, as you'll see in my weekly Technofile column at www.technofileonline.com/texts/tec040906.html. Can this be done just as easily in Mac OS X?
   Yes and no. Here's the bad news first.
   Mac OS X does not come with any built-in way to turn single clicks into double clicks the way Windows. (That would be a worthy addition to OS X, but I know of no plans for Apple to add it.)
   But there are ways to get what you want. Here's the good news, in three parts.
   1. Like Windows users, you can launch a program or open a folder -- as long as the item is already selected -- from the keyboard. Windows users do it by pressing the Enter key. Macintosh OS X users can do it by pressing Cmd-O. ("Cmd" is the abbreviation for "Command." The Cmd key is on each side of the spacebar on a standard Apple keyboard. It's sometimes called the Apple key.) Simply select an item, then, when it's selected, press Cmd-O.
   2. You don't ever have to double click to launch an application or open a folder if its icon is in the Dock. The Dock always works by single clicks. To add an application or folder to the Dock, drag the original icon (in your Applications folder, for example) to the Dock and leave it there. (To remove it, drag it off the Dock.)
   (For tips on using the Dock, read these previous articles: http://technofileonline.com/texts/mac011503.html and http://technofileonline.com/texts/mac122904.html.)
   3. Even better news: You can graduate to a better mouse -- Microsoft's wireless IntelliMouse models are the ones I recommend -- and use its special mouse software. Microsoft's software makes this easy. My main OS X Mac uses a Wireless IntelliMouse Explorer 2.0, which comes with outstanding software for setting up the standard buttons and the extra buttons on the mouse. (It has two extra buttons where your thumb rests.)
   The IntelliMouse software lets me assign a left double click to a single press of the wheel. Because the wheel rolls smoothly with a light touch, there's no danger of clicking the wheel when I'm using it to scroll. You have many other choices, too. If you don't have much use for the right button, you can assign a right click to a left double click, something I did for years before right-click context menus became as helpful as they are today.
   (Right-clicking to do a standard double click is habit-forming. If you choose it for your OS X Mac, get context menus to open using Ctrl-Click.)