It appears to be a habit I picked up along the way and misattributed to The Chicago Manual of Style. On looking it up just now, it seems that Chicago still wants those phrases to be hyphenated. I personally think, as someone posted a few weeks ago, that you have a lifetime quota of hyphens and should use them only when necessary. I don’t find any potential for ambiguity with “well” phrases, and so I’ve taken to treating them like “-ly” phrases—keeping them open except under conditions of potential ambiguity. But clearly I’m well out in front of Chicago on the point and perhaps I should reconsider.So I’m reconsidering. I haven’t changed my mind yet, but I’m willing to listen to what others have to say. Feel free to comment.
Even editors need editors.