How to Write and Speak Correctly" by Joseph Devlin is a classic reference work on the English language, focusing on grammar, vocabulary, style, punctuation, and effective communication. The book was written in the early 20th century, so some of its advice might feel a bit dated in terms of style and usage, but its core principles remain valuable for anyone looking to improve their command of the English language.Here's a summary of the topics covered by Joseph Devlin in the book:

1. Word Making and Word Meaning: Devlin dives into the origins of words, affixes, and how words can change in meaning over time.
2. Sentence Structure: This section focuses on subjects, predicates, and objects. Devlin provides explanations of the various components of a sentence and how they fit together.
3. Punctuation: Devlin goes over the various punctuation marks, like commas, semicolons, and quotation marks, explaining their correct usage.
4. Paragraph Writing: Here, the author provides guidance on organizing thoughts into coherent paragraphs, discussing topics like unity, coherence, and emphasis.
5. Formation of Words: Devlin examines how words are formed and the rules governing their formation, such as compound words, derivatives, and the use of prefixes and suffixes.
6. Figures of Speech: Metaphors, similes, and other figures of speech are discussed in this section, giving readers an insight into enhancing their language.
7. Letter Writing: A particularly practical section, Devlin offers advice on writing various types of letters, from business correspondence to personal letters.
8. Errors: Devlin highlights common mistakes in English grammar and usage, providing correct examples alongside the incorrect ones.
9. Choice of Words: This section is about diction, the importance of selecting the right word for the right context, and avoiding redundancy.
10. Speaking and Pronunciation: Devlin discusses the art of pronunciation, emphasizing the importance of clear and correct speech. He offers guidance on difficult words and common mistakes.

Remember that while the book is a valuable resource, language is constantly evolving. It's always a good idea to supplement older references like Devlin's with more contemporary guides, especially when it comes to style and usage in modern contexts.