Cách sử dụng
'Whereof' is a formal way of saying 'of which.' It is used when we want to refer back to something that was mentioned before in a sentence or in a previous conversation. For example, "The book, whereof I spoke earlier, is now available at the bookstore." In everyday conversation and writing, 'whereof' is not commonly used, and simpler alternatives such as 'of which' or 'about which' are more appropriate.