I have had several conversations lately about using mirrors while doing yoga. I come back (as I do so often) to Aristotle and the golden mean. Mirrors can absolutely help with finding alignment. "Ah, my hip is dropping and my ribs too far forward". But if we always use a mirror it can be harder to strengthen our connection to the internal kinesthetic cues. The eyes are for most of us a primary vehicle of information (just look at our language "I see" is equivalent to "I understand"). It is useful if we can connect the visual information to the body sense. "So as I externally rotate my femur I feel a certain level of opening through my ribs and pelvis." Then as we practice the posture again without the mirrors we try to use the same pathway and listen inward to find the alignment. Like strengthening small accessory muscles, rather than allowing the larger ones to do all the work.
There is also, of course, the fact that when most of us look in the mirror we do not just see our body as it is. Like a dancer draped with layers and layers of cloth we see our body with a lifetime of judgements. Seeing through all that stuff is hard. Taking it all off is harder. But if we take away the visual cue and work from within, focusing on movement, breath, and mental presence it can help at least to recognize the difference between our physical nature and our feelings about it. Maybe a better metaphor is one I sometimes use in class. It is like taking a heavy backpack off and leaving it in the cubby before class. It is so freeing to the shoulders to stretch and open and move without that weight.
The famous saying of Ch'ing-yüan Wei-hsin (Seigen Ishin):
老僧三十年前未參禪時、見山是山、見水是水、及至後夾親見知識、有箇入處、見山不是山、見水不是水、而今得箇體歇處、依然見山秪是山、見水秪是水 (The Way of Zen 220 k)
Before I had studied Zen for thirty years, I saw mountains as mountains, and waters as waters. When I arrived at a more intimate knowledge, I came to the point where I saw that mountains are not mountains, and waters are not waters. But now that I have got its very substance I am at rest. For it's just that I see mountains once again as mountains, and waters once again as waters. 13
13 Ch'uan Teng Lu, 22. (The Way of Zen 126)