It is a book written in the fifties, for people from commerce, from the military, and diplomats. When "Europeans" (the book is from Michigan) were "highly respected" in Thailand. It naturally assumes that you have servants (plural). It teaches you to use "tahn" for "you". This is not only wrong, it would not be appreciated by many Thais if you address them as "tahn" (which is pronounced short BTW, even today's textbooks tell you it is long). Tones are often not marked. That's like a textbook of English not writing the vowels. 'nuff said