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I have come across a book Japanese in 30 hours by Eiichi Kiyooka published in 1942. On page 5 it gives an example of a sentence This is not a book. translated as
However, when looking at contemporary resources I find instead
When is でありません used and when is ではありません used instead? Or does でありません sound obsolete in contemporary Japanese? How would it sound if I used it in conversations or in official situations?
Note that the book also uses わたくし instead of わたし. I find the book the most efficient textbook of Japanese I have ever seen. Hence I do not mind if while as a beginner I sound too old-fashioned. But could my old-fashioned use of language cause some cultural blunders?