This is taken from Pedro de Alcantara’s fabulous book, Indirect procedures: a musician’s guide to the Alexander Technique:

     We tend to be concerned with symptoms and effects, and less concerned with their causes.  For instance, “my shoulders are tight” points to an effect. “I’m tightening my shoulders” points at a cause.  Let’s call the effect your functioning, and the cause your use.  They’re very intimately related: your shoulders will stay tight as long as you tighten them. This sounds like wordplay, but it states a deep truth.
Alexander wrote that “the influence of the manner of use is a constant one upon the general functioning of the organism in every reaction and during every moment of life…From this there is not any escape.  Hence this influence can be said to be a universal constant in a technique for living.”
How you use yourself affects how you function.  If something is wrong with your functioning – for instance, if your shoulders feel tight – you need to change how you use yourself, which means how you react to the world around you and to your own thoughts and desires.  It’s not your shoulders that give you trouble, but you who give them trouble.
In every aspect of your life, you’ll end-gain if you work on your functioning. The only practical approach is to work on the use that regulates and determines the functioning.  As Alexander says, from this there is not any escape.
A voice teacher asks her pupil “to sing in the mask,” or “to bring the tone forward.”  A singer who sings in a certain way might subjectively feel as if she were placing her tone forward, but this would be a result of her singing technique rather than a technique in itself – an effect, not a cause.  Frederick Husler and Yvonne Rodd-Marling wrote:

The sounding of a resonance chamber [in this case the so-called mask] is always a secondary manifestation, the result of muscle movements in the vocal mechanism…It goes without saying that the first causes for the various acoustic phenomena that occur in singing lie in the vocal organ itself, and it is these that the voice trainer must learn to hear.

The sounding of a resonance chamber is an aspect of the singing voice’s functioning. It may be more productive to leave the mask alone and work on those aspects of your voice that are more accessible to actual control – for instance, the combinations of pitch, vowel, and intensity that create sounds and vibrations that give you the sensation that you’re singing in the mask or placing the tone forward.

De Alcantara, Pedro. Indirect procedures: a musician’s guide to the Alexander Technique. Oxford University Press, 1997.