Two marks of punctuation, square brackets and the ellipsis mark (three spaced periods), show readers that you have added or omitted words from a quoted passage.
Brackets are used for additions or clarifications, as in the following example from a paper on Alice Walker’s short story “Everyday Use.”
Mama describes Dee as “lighter[-skinned] than Maggie, with nicer hair and a fuller figure” (289).
Because some readers might not understand the meaning of lighter out of context, the writer has supplied a clarification in brackets.
Brackets are also used to change words or letters to keep a quoted sentence grammatical in your context, as in this example, where the writer wishes to avoid a tense shift.
When Rita sees Johnny’s relaxed attitude, “she blushe[s], like a wave of illness” (159).
The ellipsis mark is used to indicate omissions. In the following example from a paper on Charles Baxter’s short story “Gryphon,” the writer has omitted some words from the original in order to keep the quoted passage brief.
With a straight face, the substitute teacher, Miss Ferenczi, tells the fourth-grade class, “In higher mathematics, . . . six times eleven can be considered to be sixty-eight” (130).
If you want to omit one or more full sentences from a quotation, use a period before the three ellipsis dots.
When a student announces that Mr. Hibler always begins class with the Pledge of Allegiance, Miss Ferenczi replies, “Oh, does he? In that case you must know it very well by now, and we certainly need not spend time on it. . . . A pledge does not suit my mood” (129).
Use brackets when you change a letter from capital to lowercase or vice versa to fit into your sentence. See the example here.
Related topics:
Using quotations appropriately (MLA)
Using the ellipsis mark to limit quoted material (MLA)
Using signal phrases to integrate sources
Using MLA style for citing literary works