It's one of the many white, fall-blooming asters. At least they used to be asters; many of them have been moved to genus Symphyotrichum. Yours may be Symphyotrichum lateriflorum (but that is just a guess as there are many very similar species).
I'm pretty sure it's a Symphyotrichum (formerly Aster) sp. Years ago I remember helping a friend ID some plants for a course she was taking for fall semester. The plants samples had to be fresh and locally grown... so we ended up with more than one of the asters. It was a real pain to ID them, even with a detailed key book... had to note the plant's habitat, measure height/spread, etc. and then for the fun part... dissect the flowers and measure and count each part including petals/rays, pappus, etc. I wouldn't even attempt to ID an exact species from a single photo.
This time of year and those leaves and the bloom description say common name" Willow Aster". I have these and love them hanging over the Coneflower stalks, Pretty weed for an invasive ,Bees and Butterflies love it