There is one exception to the statement that every word in a verb phrase must be a form of a verb. The word to, which is neither a verb nor a verbal, is sometimes found in a verb phrase as in the sentence, She seems to be truthful. Here the verb phrase seems to be is used instead of the verb is to express doubt. It contains the verb seems and the verbal be, which is preceded by the word to. This little word is so often attached in this way to the root form of the verb, when this form is used as a verbal, that it seems almost to be a part of it, and is sometimes called the "sign" of the verbal. (§ 65).