The Higher Self
The easiest way to relate the concept of Sagittarius is to say the world beyond what you know. It is the world of potential experience. So if you want to take a trip to a new place, we have the Sagittarian theme of the long-distance journey, but also the potential of experiencing something, and someplace (and its people) new.
Now, thinking out loud here for a sec, that concept looked good in my notebook, but I remember now that Sagittarius is also the world of accumulated knowledge, the university library, for instance. So maybe we could say that to experience Sagittarius we are existing on the border between the known and the unknown. That's a good image for the line across the arrow in the symbol for Sagittarius, which points beyond the border to the larger world.
We tend to think of Sagittarius as the sign of anything spiritual, the world of ideas beyond what we normally think -- including spirituality, as opposed to organized religion (which most people would associate with Capricorn, because of the structure involved). This was true long before we knew that the center of the Milky Way galaxy (where we live), which is like saying the center of the local universe, was located in Sagittarius. (That is true, and the Sun and Earth align with this day each year between Dec. 17-20)
"Humanity has always projected its potential for higher conscious onto the heavens in one way or another," Melanie Reinhart said at a workshop a few years back, adding a few more comments about the nature of the expanding cosmos that I will pick up on soon.
Higher consciousness in any form is precisely the issue of Sagittarius. It is the sign of what some people call the Higher Self, which can manifest in our experience in ways described by planets in and ruling Sagittarius and its associated house, the 9th. For most people, we take much of this infomation as describing their God-concept, but with Sagittarius and the 9th we can look for where the God concept and the Self concept merge into one.
This is the Higher Self, the true self, the highest potential of who we are, as opposed to the ego, who is a dangerous fellow when he thinks he's God.
Who is this Higher Self? It is that version of us who we become who we knew we always were. It's the person we grew into and at the moment of growing in, we feel that we had the potential all the time. The 'lower self', you could say, is the aspect of who we are that believes in limitations that are not there, who does not see or pursue the possibilities and has a limited sense of its own potential. The Higher Self is that potential being wihin us, which usually needs to be accessed through some kind of growth process... and yet he or she was there all along, watching us, and waiting for us to notice.
This is view of the human mind in its current state in our culture, stated as spiritual psychology. Or, you could just as easily say the Higher Self is that formless, timeless expression of You that you discover in the midst of orgasm, if you are fully awake and aware in that moment.