Consider this picture by j neuberger ---it has the appearance of being an abstract modernist photography concerned about its own form: colour, line, frame, surface etc. It says purity of the photography.
Look closer. Note the organic form of the trunk of the tree. A tree! Tht shouldn't be there. Abstract modernism is premised on the rejection of naturalist representation. And there are twigs hanging down. There is movement and flow in the picture --a form of dynamism or becoming that takes us outside the modernist frame into postmodernism. This flow or movement coupled with the representation of objects within an abstract photography is a transgression of modernism.
You can see the transgression when the image is compared with this one