As always, unless I hear otherwise I will assume you understand the readings from The MIT Guide to Science and Engineering Communication. Therefore, lectures on readings from the book will tend to be short, focusing on specifics I want to highlight. If you have any questions or need further elaboration on anything about the readings, including material not covered in the lectures, please ask.
Distinctions between Letters and Memos
As the book explains, letters and memos differ in a few key features. One is how they are formatted. The other is context: letters are usually considered more formal and are used for external communication (that is, communication with people outside your organization), and memos are usually considered less formal and used for internal communication (that is, with your co-workers).
One of the reasons why letters are used for external communication is that they are considered the more formal genre. This is very much an issue of decorum, and decorum itself has long been a rhetorical issue. Because letters are more formal than memos, letters are sometimes used for internal communications as well. Whereas a supervisor may send out an organization-wide memo congratulating someone on a job well done, that same supervisor believes the accomplishment is worthy of a personal communication as well, they will likely send a letter of congratulations to the individual rather than a memo. The same can apply to a thank you, a memo to publicly thank the individual or individuals but a letter to thank them personally.
External vs. Internal Contexts
While it is quite rare and entirely unusual to send a memo to someone outside your organization, what constitutes your organization can be at times fluid. In large, multi- organizational or institutional projects, it’s quite common to find yourself on a team or reporting directly to individuals who are not part of your organization. In that context a memo may be more appropriate than a letter.
As the book notes, email has no firmly defined status. In many instances it can be less formal than either a letter or a memo and is good for quick, informal communication such as a quick, informal update or clarification, a follow up to a meeting, a quick response to a letter or memo, etc.
While we can think of email as its own genre — the genre of quick, informal correspondence — email is also a medium of transmission just as paper is a medium. Email can deliver a letter or a memo as an attachment, and the email itself can serve the function of a letter or a memo. When the purpose of an email is transmission of an attachment, include a brief note as to what is being transmitted and why, along with a salutation and a closing. When the email is the letter or memo, follow the conventions of the letter or memo genre.
Formatting Letters and Memos
While the MIT Guide offers some guidelines on how to format letters and memos as well as some examples of both, Purdue University’s Online Writing Lab (OWL) offers detailed guides to writing and formatting letters and memos.