The diagram of a simple sentence begins with a horizontal line called the "base". The subject is written on the left, the predicate on the right, separated by a vertical bar which extends through the base. The predicate must contain a verb, and the verb either requires other sentence elements to complete the predicate, permits them to do so, or precludes them from doing so. The verb and its object, when present, are separated by a line that ends at the baseline. If the object is a direct object, the line is vertical. If the object is a predicate noun or adjective, the line looks like a backslash, \, sloping toward the subject.