That looks suspiciously like a Fukien tea (Ehretia (or Carmona) microphylla), a tropical tree that would never be growing outdoors in MI! Is it in fact something you found in the ground, or in a pot?
Philadelphus lewisii (or a similar species) or mock-orange. For a Chinese relative comparison that shows both flower and bud, see Philadelphus delavayi
Ah, you're right Ginger Blue (and I'm wrong) - Philadelphus only has 4 calyces for one, and doesn't have that kind of inflorescence for another.
This shot was tricky, it does look like a mockorange. One with open flowers would have been better. If it had been a mockorange I think it would have been a different species, however, being in Michigan--unless able to grow in cultivation back there. Philadelphus lewisii does not range natively east of Montana.
I was going off the leaf characteristics re: the species - I had found a Michigan site mentioning P. lewisii in cultivation. Ah well, I know better for next time.
Western mockorange leaf comes to a point at tip, plus margins do not have such forward-pointing teeth (lobes?)--looks more like a kite. And its leaves are opposite, of course.
Well, that, and in that part of the country right now, every third lawn has one getting ready to bloom. Often, knowing the location and time is as important as anything else in these IDs.
