Alexander Technique is often associated with improving posture. And certainly people that study with an Alexander teacher over time frequently show physical changes that others notice as improved posture.
When speaking to people about what I do, I often say that I help my students change poor postural habits or improve their posture. I use the word posture because it is a word most people have heard before. Most people have some notion of what posture is about.
However, here is my dirty little secret: yes I do help people with their posture, but not by helping them with their posture.
I help people with their posture by helping them better understand, improve awareness of and develop strategies for changing their Use.
Every field of study has its vocabulary. Use is one of those special vocabulary words that belong to the Alexander Technique.
When you work with an Alexander teacher you learn a different approach to solving your problems. A different approach requires different thinking and some new ideas. So, some new vocabulary.
Your Use is how you support and coordinate yourself while in movement or at rest. Your Use is how you do whatever you do, in a very broad sense. And whatever you do has a physical component, a mental component and an emotional component—it involves the Whole Self (which as you guessed is another Alexander vocabulary word).
Your Use is influenced by your thinking and by your emotions.
To bring about changes in your habitual patterns of Use you must be willing to be more conscious of how you think and react.
If you try to improve your posture by just sitting or standing up straight you are missing a whole lot of what is influencing your posture for good or ill.
Study of the Alexander Technique is a study of the Use of Yourself.