The reasons that i feel that all these story's show modernism would be they are all alike in a sense. They all speak about the future and how horrible it is going to be. And just being abruptly short. Also is shows the different techniques of writing that has evolved. Such as in Fahrenheit 451 he always uses run on sentences to give you the allusion that you're out of breathe.
One of the main points that makes this a modernist novel would be the imagery. In both of the stories they both portrait imagery. Such as in Richard Cory. They give you this image of a great guy that everybody wants to be alike , but then he abruptly kills himself. This was very suttle when the author told us this. It just ended and that gives you more time to think about what the centeral message is.
Also another for of modernism in these novels would be the allusions. In Fahrenheit 451 the author uses the allusion of you being out of breathe. He does this by making guy montag use run on sentences. This makes you short of breathe while he is also short of breathe. It gives you more of an understanding on how the character in the novel feels
Lastly it is about the future and what it withholds for us. The main thing is , is that it is never even a good thing. It is all bad and dreadfulness and pain and misery I feel like the authors used that kind of writing to make the reader think that life is short. That you should go out and do something with it and not just waist it like its trash because everybody has a meaning to life. You just have to figure out what yours is.
These are the main reasons why I think that all these novels involve modernism.