Is This A Beautiful Flower… Or A Horrible Weed?

There's some type of plant that has sprung up in the flower bed in our front yard, but we can't figure out if it's a plant... or a weed.

The previous owners of our house planted a very nice, landscaped flower garden in our front yard. And they filled it with all manner of lovely perennials, which mean they pretty much bloom every spring, all by themselves.

Which is great. Less work for us! Sure, we do a little raking and spring cleaning, but for the most part, they all bloom each spring regardless of what we do.

But there's one plant with which we're having a tough time. And by that, I mean, we can't tell if it's actual flowering plant-- or is merely a weed that's taken over that part of the flower bed.

When I was out adding mulch earlier this spring, the mystery plant (or weed) had yet to flower. Which made me think it was a weed. That, and its leaves looked more weed-like than flower-like, we thought.

Now, though, there are some lovely purple blooms on the mysterious plant (or again, weed), and it looks much more like a  flower than before.

So, we're stuck still wondering. I tried looking up 'purple flowering plants in Minnesota' on this Minnesota Wildflowers site, but there are 229 pages of flowers! Yikes.

So what do you think? Is it a lovely plant... or a horrible weed?