Difference between combine and union?

Combine makes 2 or more paths into a compound path with 2 or more subpaths. This means that they all share the same style (color, opacity, stroke width, etc.). The paths may be open or closed.

Union typically results in one closed path, although not always. Like most of the path operations, it works on areas. It takes the area inside one closed path and the area inside another closed path and puts them together, resulting in one closed path. While you could use it to combine simple open paths, that's not the main purpose.** In Help menu > Tutorials > Advanced, there's an overview of the path operations (also called Boolean operations), and here's the info in the manual http://tavmjong.free.fr/INKSCAPE/MANUAL ... ining.html.

I never thought about it before, but I guess they are very similar. I'll be interested to read other replies here

**In doing some testing, out of curiosity, I discovered something strange. I didn't think you could take 2 open paths and use Union on them. I thought nothing would happen. But it does appear to combine them. Next I was going to use the Pen tool to continue one path and join it to the other, just to find out if they behaved the same way as if they had been combined. But they don't display handles with either Pen or Pencil tool, as they would if they had been Combined. Even after using Path menu > Break apart to separate them again, I find that those 2 paths (simple, 2 nodes each) don't display handles. (I mean the tiny square where you place the mouse to continue a line with Pen or Pencil.)

So clearly Union does something similar to combining, but it looks like some properties may have been lost. So for node editing, you should definitely use Combine. Even though Union appears to combine them, some properties appear to have been lost.

Again, I'll be interested to learn more about this