Action and motion can be evident or implied by the context of an image. We can use a fast shutter to freeze action, we do this where action or motion is evident.
We intuitively know that there is motion in this image, a stationery train would not do that to snow. Image from Headingley, Manitoba 2013.
Here we intuitively understand that the birds are in motion, that posture and remaining airborne are mutually exclusive. Image from Rincon de Guayabitos, Mexico 2019.
Motion is evident in this image because logic dictates that the ribbon cannot maintain that shape without the action of the person holding the wand. Image from Beijing, China 2018.
In contrast, we use slow shutter speeds to emphasis motion where motion is not evident.
The gate is down, the warning lights are flashing, and that damned bell is ringing. But is the train moving?
Composing with a slower shutter speed blurs the train leaving little doubt that it is, in fact, moving.
jnicklin photography 