The following is a fairly formal reply to an invitation. Suppose the writer and the recipient were intimate friends, the words of the reply would be quite different even though the purpose and the content remain unchanged. Rewrite the letter as an informal reply (letter). Dear Professor Smith, Thank you very much for the kind invitation to dinner. I regret that my wife is ill so that it will not be possible for us to come. I do hope, however, that I shall have an opportunity of seeing you again in the near future. Yours sincerely, Tom Jackson