Know What You Know
Read John Friend's response:
Ideally, we should only teach what we understand and have confirmed through our own experiences. However, teachers often present information that they have gained through the teachings of another, without testing it for themselves. A teaching that is accepted as authoritative without proof is called dogma. To avoid being dogmatic in our teaching, we need to question authority and test the information ourselves. In turn, it is important to encourage our students to test our teachings before accepting them fully.
It's best to practice a teaching for an extended period of time, testing its integrity before disseminating it. Over time, you will feel validated in a deeper understanding of the knowledge you've gained. If the teaching shows inconsistencies when you are testing it, then its integrity is correspondingly weak. Teach what you know, through your own experience of extended practice, to be valid.
At the same time, it is difficult to ever completely prove the absolute truth of a teaching. And if we were to wait until we had totally proven the teaching through our own practice, we would probably never teach! Consequently, we must still put some trust in our teachers and the style with which we are affiliated. However, as soon as a teaching is shown to be invalid, then we must inform our students and drop that teaching from our method.
For example, years ago I developed a system that I call Universal Principles of Alignment. I practiced and tested the alignment principles in a wide variety of poses for two years before I started teaching them as a system. I analyzed the set of principles in every possible pose that I could imagine. These principles were different than what I had been taught and different than much of what was published—but they were valid for me. Since I did not experience any inconsistencies with them, I began to teach these principles with confidence. Thousands of students around the world have applied the Universal Principles of Alignment to their poses and found them to be consistently effective, but I must stay open to the possibility that an inconsistency may be found. A key part of yoga practice is to remain open to the knowledge that what I hold to be true today may not be true tomorrow.