Singers must understand that, what is necessary for vocal improvement is change, and that this change is the result of what is technically perceived to be better. Without change the singer can only expect to perpetuate her vocal faults. In the search for vocal improvement there is always varied opinion of what is right and wrong and the student can become confused. It is always wise to pay attention to criticism, consider the sources of opinions, then permit the passing of time for testing the suggested theories. Remember that correct progress is always reflected in the ease of vocal production, the overcoming of difficulties, and a positive response from your listeners.
Frisell, Anthony. The soprano voice. Bruce Humphries Publishers, 1966.