"There are various kinds of untruth. There is an absolute untruth, an untruth in itself, that no addition or qualification can make true: as, if a man says a thing he saw was black, when it was white, as he remembers and knows. So, as to knowing the truth. A man may know it, and yet it may not be present in his mind at the moment of speaking; or, if the fact is present to his mind, it may not occur to him to be of any use to mention it. For example, suppose a man was asked whether a writing was necessary in a contract for the making and purchase of goods, he might well say "Yes," without adding that payment on receipt of the goods, or part, would suffice. He might well think that the question he was asked was whether a contract for goods to be made required a writing like a contract for goods in existence. If he was writing on the subject, he would, of course, state the exception or qualification."