Josephine Turck Baker's turn-of-the-century periodical, Correct English -- subtitled A Monthly Magazine Devoted to the Proper Use of English -- featured regular "conversations" in which "Mrs. B" instructed various (strangely docile) friends, acquaintances, and children in improving their speech. In the issue for January 1, 1900, poor Mrs. A. played the role of pupil:
Mrs. A. -- I am so pleased to find you at home. I feared you might be away as it is such a beautiful day. I want to ask you some questions in regard to the article on Words and Their Uses, which appeared in the last issue of Correct English.
Mrs. B. -- I am very glad you came to-day. You will always find me at home on Wednesday as I reserve that day for my friends. I notice that you say, "I am so pleased to find you at home." Did it ever occur to you that so does not express any meaning in that connection?
Mrs. A. -- I never thought anything about it. Is "I am so pleased" an incorrect expression?
Mrs. B. -- Yes; because it is a meaningless one. It is a colloquialism, and, in consequence, is permissible only in familiar conversation. I object to it because it is an incorrect use of so. Of course when one says, "I am so pleased," or "I am so delighted," or "I am so disappointed," one means I am extremely pleased, delighted, or disappointed, as the case may be. But that is a perversion of the use of so. It is better to substitute "very much," or "extremely."
Mrs. A. -- Is it incorrect to use "so" with an adjective, as, for example, "You are so kind," "We are so happy," "It is so nice of you to come?"
Mrs. B. -- All those expressions are colloquialisms; so being used in each case to mean extremely, or very. As I said before, strictly speaking, these are perversions of the use of so. As a rule so should be used only when the degree is specified, implied or understood. This requires a subsequent or explanatory statement, or the degree may be indicated by previous statements or by the circumstances of the case. Thus, we correctly say, "I was so delighted with the work that I paid the bill without any question as to its correctness," or we may say, "She sang so beautifully that every one was delighted with her voice."
Mrs. A. -- To say, "I am so delighted" does sound senseless and if it is only sanctioned in familiar conversation, I think I shall avoid it altogether.