Syntatic Truism 4

An example of a parallelism in rhetoric (quite similar to the semantic Truism(s) 4 a,b,and c) is the following:

The sky was red
The car was red
Her lipstick was red
But the blood was black against the snow

Wait, that's not right, isn't that just 4A? How about...

Artic Terns migrate
Swallows migrate
Robbins used to migrate
But now they are around all winter

With the use of "but" these clearly are using implicit assumptions of some kind. Is it just a byproduct of parallel phrasing or is it more? I am wondering about the sudden and spontaneous conversion of the word "migrate" into a category from which we can say the last line of the stanza is excluded.

Exclusion from a category is hardly the stuff of proto semantics. So for now let's go with this: parallel phrasing can create categories and a higher level truism accompanies the lower level Trusim 4: It says if "X in category" then also the next "Y in category".