At the beginning of the letter, Martin Luther King makes his points with brevity and elegance when he employs double antithesis in short, gnomic phrases:

Injustice anywhere is a threat to justice everywhere.

Here, in a sentence of eight words, King has the antithesis between injustice and justice, as well as the contrast between anywhere and everywhere. The grammatical parallelism heightens the rhetorical effect. He repeats the structure in another memorable phrase, which sounds like a proverb:

Whatever affects one directly, affects all indirectly.

King later uses the same dual structure as an elegant way to conclude longer sentences, as when he observes:

We know through painful experience that freedom is never voluntarily given by the oppressor; it must be demanded by the oppressed.

The use of antithesis is frequently varied throughout the letter, exhibiting King's mastery of pace and rhetoric. The three examples above are all dual antitheses. These give a stately balance to the phrase, reminiscent of the great prose stylists of the eighteenth century. However, a single antithesis is pithier, and can be expressed in fewer words, such as the final four of this sentence:

Too long has our beloved Southland been bogged down in a tragic effort to live in monologue rather than dialogue.

Sometimes, however, King takes the opposite approach, expanding his sentence into a long, drawn-out antithesis or series of antitheses:

Thus it is that I can urge men to obey the 1954 decision of the Supreme Court, for it is morally right; and I can urge them to disobey segregation ordinances, for they are morally wrong.

Here we have three antitheses in the same sentence: obedience and disobedience, the two different laws and, finally and most powerfully, the simple contrast between right and wrong. There are many more examples, including King's frequent contrasts between justice and injustice, often in parallel sentences:

One has not only a legal but a moral responsibility to obey just laws. Conversely, one has a moral responsibility to disobey unjust laws.

The continual use of antithesis to highlight moral contrast is one of the most effective devices King employs in the letter, creating many memorable phrases still quoted by activists in a range of causes today.