Which figure of speech is used in this text?
We must learn to live together as brothers or perish together as fools.
—Martin Luther King, Jr., 1964 commencement address at Oberlin college

 - antithesis
 - assonance
The text uses antithesis, the contrasting of opposing ideas within a parallel grammatical structure.
King contrasts two parallel phrases, live together as brothers and perish together as fools.