Final answer:
Parentheses are used to provide additional, nonessential information in a sentence with less emphasis than dashes or commas. They are useful in a variety of contexts, including quotation modification, chemical structure representation, and in-text MLA citations.
Step-by-step explanation:
Parentheses are indeed used both in the Tabular List and Alphabetic Index to provide additional information about the main diagnostic term. They help by setting off nonessential material, such as dates, clarifying information, or sources from a sentence, without placing as much emphasis on the enclosed content as commas or dashes would. This technique of downplaying content helps maintain the flow of the main text while still offering readers access to supplementary details. When it comes to punctuating quotations, another practice related to parentheses is the use of brackets ([]). These are used to show any changes made to a quotation, such as Abruzzi cited the study, noting that "[t]he results provide hope to patients [with muscular dystrophy]." This indicates that the quoted material has been altered for clarity or to fit the grammatical structure of the surrounding text.
Moreover, in scientific writing, such as chemistry, parentheses in condensed structural formulas indicate that the enclosed grouping of atoms is attached to the adjacent carbon atom, serving a key role in conveying chemical structures. Similarly, in-text parenthetical citations in MLA formatting tell readers where to find the source information on the Works Cited page.