: Why do we have to expand before merge? I am a beginner in Adobe Illustrator. In a project I was doing on Treehouse, I got stuck when the instructor told me to expand and then merge without

@Turnbaugh909

Pathfinder doesn't work with strokes or other appearance attributes or effects; it only works on the underlying paths. So if you want strokes or other appearance attributes to be accounted for in Pathfinder operations then they need to be expanded first. Keep in mind that once expanded you can no longer modify or remove them though; they're "baked in" to the actual paths.

A quick example...

A simple circle and square with a stroke (originals on the left; the result after running the Pathfinder operation on the right), merging the shapes simply removes the strokes:



If we outline the stroke first (via "Expand"), the stroke is left intact:

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