This 4 petaled flower is growing in partial sun, slightly on the moist side. Stalk is 2 to 5 feet high. Blooming in May in Oregon. Flowers range from white to medium lavender and have a slight pleasant fragrance. Don't know if is a self-seeding annual or a perennial that dies back in winter.
Actually, I think this is Dame's Rocket, Hesperis matronalis. It has a four-petaled flower that is white or lilac and fragrant, blooms May-June in most places, 1-3 feet tall, with oblong, toothed leaves that alternate up the stem.
This is an escaped ornamental garden plant and is listed as a noxious weed in most (if not all) of the US. It reseeds very easily, and spreads this way. I know in our area it is hard to get rid of, because people love it and are hesitant to pull it.
Well it appears to be Lunaria, common name Honesty or Moneyplant, (the latter name coming about because of the coinlike silver seedcases) most likely Lunaria annua, which is naturalized in your region, and does come in white and this deep purplish pink, and lighter pink. However, the leaves up the flowering stem are a little longer and narrower than those we see here in the UK, where this plant is indigenous, which gives me a little doubt. Images below of various colours and of the seedcases
And you may be interested in the following
There are cultivars available for purchase of this plant, and the flowers on those may be more prolific, and in stronger colours, but always in the white through pink to purple range.
Now I've seen the other answer, mine's wrong, that one's (Hesperis matronalis) is right.