When you drag a bunch of items into a folder in the Finder on your Mac and some of the items in there have the same name, your Mac will ask you if you want to replace the items in the folder you’re dragging to. This is all well and good when you’re trying to do just that, but what about when you want to merge the files from the first folder to the second?
Well, it’s amazingly simple.
Create or find a couple of folders on your Mac that you want to merge. You can drag a bunch of files from one folder to the other, and see the Replace dialog that typically comes up when you do so: Skip, Stop, or Replace. If you want to put all the non-conflicting files in, hit Skip. If you want them to replace the items in the destination folder, choose Replace. If you want to cancel the whole process, use Stop.
Hit Stop to cancel the process, and then try this:
Hold the Option key down when you drag the files into the second folder. You’ll see a green Plus image appear when the mouse hovers over the destination folder. When you release the mouse button to start the merge, keep holding down the Option key. You’ll then see three choices: Stop, Replace, or Keep Both. To merge the folders without replacing anything, click on Keep Both.
This isn’t as intuitive a name as Merge, which was what this feature was called in OS X Lion, but it’ll do. Just be sure to keep holding that Option key down or you’ll see the standard three choices.