
Max M. answered 04/25/19
Harvard Literature major with 20 years of coaching writers
Without context, I'm not totally sure I understand your question, so this may be way off-base, but here's my best shot:
I'm guessing that by cohesion, you mean that you are getting feedback that your writing is all over the place and it's unclear how different ideas relate to each other. And if so, you're asking how antonyms can be a tool to address that problem.
Antonyms, as you probably know, are words with opposite meanings, so putting them close to each other--either in the same sentence or the same paragraph--can emphasize a relationship between two ideas, and thereby link them, so as to achieve cohesion.
As an example in a lit. crit. paper, you might be asked to discuss Macbeth's relationship with fate. Maybe at first, your thesis statement is something like, "Early in the play, Macbeth is confused by fate when the witches tell his future, and later in the play, he is glad to see the predictions come true, but finally, the words of the apparitions come back to haunt and destroy him." Not a very cohesive statement. But you could rewrite it to something like, "The cryptic, misleading words of the supernatural characters lead Macbeth to both embrace and fight his fate throughout the play." Putting antonyms "embrace" and "fight" next to each other helps tie the idea together.
In a history paper you might write about how "the Industrial Revolution provided an increased standard of living for the wealthy, but a greatly diminished one for the working class," which would tie your paper together more than just writing about those effects independently of each other.
Even in a science paper, you might, instead of simply listing the various behaviors of a species, write that "they show aggression under circumstances X, Y, and Z, but submissiveness under conditions A, B, and C."
Hope this helps! Feel free to reach out if I misinterpreted your question, or if you have follow-ups.