Three fairly distinct types of method may be defined, depending on the class of materials adopted. At one extreme are found those teachers who attempt to follow strictly the scientific principles. These teachers generally profess to employ only the purely mechanical doctrines of Vocal Science, and to ignore all empirical interpretations of these doctrines. They generally devote a portion of every lesson to toneless muscular drills, and insist that their pupils practise every exercise in singing, with special attention to the throat action. These teachers attempt to follow a definite plan and order in the giving of exercises and rules. This systematic arrangement of instruction is, however, seldom followed out consistently with any one student. An important reason for this is considered in Chapter I of Part II. A very different type of method is taught by many teachers who pay special attention to the empirical topics of instruction. Of course no teacher professes to teach empirically; on the contrary, every method is called scientific, no matter what materials it embodies. Indeed, a very little attention paid to breathing, attack, registers, and nasal resonance, is enough to relieve any teacher of the reproach of empiricism. The teachers now being considered touch to some extent on these topics; but most of their instruction is based on the traditional precepts, the singer's sensations, and the special vowel and consonant drills. In the first few lessons of the course they usually give some special breathing exercises, but almost always ignore breath-control. Not much is done for vocal control in the strictly muscular sense. Special "voice-placing" exercises are not used to any such extent as in the strictly scientific methods just described, the voice-placing work being usually done on vocalises, songs, and arias. No system whatever is followed, or even attempted, in the sequence of topics touched upon. The directions, "Breathe deeper on that phrase," "Bring that tone more forward," "Open your throat for that _ah_," "Feel that tone higher up in the head," may follow one after the other within five minutes of instruction. Teachers of this type are frequently charged, by the strict advocates of mechanical instruction, with a practice commonly known as "wearing the voice into place." This expression is used to indicate the total abandonment of system in imparting the correct vocal action. It means that the teacher simply has the pupil sing at random, trusting to chance, or to some vague intuitive process, to bring about the correct use of the voice. To the vocal scientist, "wearing the voice into place" represents the depth of empiricism.