'Practical English Usage' (3rd Edition)
by Michael Swan

(The world's most trusted guide to problems in English)
My English lecturer recommended this book to me, and I have never regretted buying it. As a non-native speaker of English, I find this reference book to be very straight forward and answers most, if not all, of my questions on English. The differences between formal written English, and informal written English are clearly explained, and there are a lot of examples too. As a non-native speaker, the part on the differences between British and American English is greatly appreciated. On top of that, entries on pronunciation, punctuation marks, idioms, taboo words, slang, spelling and others are also available. It is also very user-friendly as there is a solid index, and a cross-reference to related topics. I would recommend this book to those who are studying English in the elementary level, as well as the advanced non-native speakers as one will never fail to learn something new whenever one opens up the book.
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Practical English usage