Brackets allow you to insert your own words into quoted material to explain a confusing reference or to keep a sentence grammatical in your context.
According to Albert Castel, “It can be reasonably argued that he [Forrest] was justified in believing that the approaching steamships intended to aid the garrison [at Fort Pillow].”7
To indicate an error in a quotation, insert [sic] right after the error. Notice that the term sic is italicized and appears in brackets (see an example).
If you use [sic] to indicate an error in your quoted source, be very certain that it truly is an error and that you know the correct form.
If a source is filled with errors, as is the case with many historical documents, this use of [sic] can become distracting and is best avoided. Readers will recognize that the unconventional spelling or grammar is part of the original source. Be very careful when transcribing to be true to the source text.
Exercise: Integrating sources in Chicago (CMS) papers 1
Exercise: Integrating sources in Chicago (CMS) papers 2
Exercise: Integrating sources in Chicago (CMS) papers 3
Exercise: Integrating sources in Chicago (CMS) papers 4