Based on the idea that the principles of effective communication are the principles of good letter writing, Plain Letters is a very thorough and sensible handbook for writing business letters. The author begins by outlining what she calls the 4-S virtues of plain letters: shortness, simplicity, strength and sincerity. She advises the writer to avoid generalities and abstractions, to make letters positive, to be natural, and she suggests ways to avoid saying too much by economizing on words and eliminating cliche prepositional phrases. She stresses the necessity of the writer knowing his subject so well that he can discuss it confidently, saying only what needs to be said, in a conversational tone. Sections of the book are devoted to the practical matter of grammar with emphasis on the troublesome comma; style in letter layout and design; managing correspondence so there will be more time for shorter and better letters; and plain letters exemplifying some common purposes of business writing.