If they can't, what is the difference between them? When have we to use the tag 'publication' instead of 'publishing'?
The words themselves have a slightly different meaning, but in terms of the way these tags are used, there's no real difference between the tags.
I'd have no trouble making one a synonym of the other, unless someone else has an objection. It'd make it easier to find questions with these tags, I think.
Edit: Have created and approved the tag synonym.