There may be times when you need to add or alter words in a quotation, so that it will make sense in the context of your essay. For example, here we rave added a character’s name to help the quotation make sense: Malcolm muggeridge said that ‘[Macmillan] exuded a flavor of mothballs’. Square brackets are used around the interpolated matter. You might also need to alter a quotation if you are using a quotation with a lower-case letter at the [outset, but want to use it to start a sentence:
(T]he lady’s not for turning’ is just one example of Margaret Thatcher’s striking use of literary allusions for political ends.
Square brackets show that material has been added or altered. As we have noted above, ellipsis marks (three stops) have the opposite function, indicating an omission from a quotation:
a man … is so in the way in the house. (Elizabeth Gaskell)
If you want to omit a line or several lines from a poem you are quoting, you put an ellipsis at the end of the previous line before the omission, as in this example from Donne:
Busy old fooled, unruly sunned … She is all States, all Princes
As with all such devices, the best advice is not to over-use them, but they are worth knowing about because they are used in academic writing and it is as well to understand the conventions you are working with. It is the case, though, that you could write hundreds of essays and never encounter a single occasion on which you needed to edit a quotation in the ways described. They are usually changes made necessary by the context in which they are placed. Really, this is another case where, as with so much in presentation, a little bit of common sense together with consistent usage will see you through.
References
Whenever you quote, or use material from a source, you need to provide a reference, showing the source of your quotation or information. This would either appear in parentheses at the end of the quotation or relevant sentence, or would be footnoted, or as an endnote, a number in superscript signaling the note. We thought long and hard about whether to include advice on references, but decided against it, as the conventions vary from subject to subject. You will probably have been provided with a style sheet for references as part of your course and you will need to follow whatever recommendations are given in it.