Final answer:
In MLA citations, include a work's title when citing authors with the same last name or when the work has no known author; for the former, initials and last names are used, for the latter, abbreviated titles in parentheses suffice.
Step-by-step explanation:
In an MLA parenthetical citation, it is necessary to include part of a work's title along with the author's last name when there might be confusion for the reader. This can occur in situations such as when authors with the same last name have written different works that you are citing within your document. In such cases, initials along with the last name are used to differentiate between the authors (J. T. Greene 21; M. Greene 30).
Another instance where you would include part of a work's title in the citation is when the work has no author. Here, you would use a signal phrase with the work's title or an abbreviated version of the title in parentheses, along with the page number if available ("Abbreviated Title" 21). Titles of articles are put in quotation marks whereas book or journal titles are italicized to adhere to MLA formatting guidelines.