Yin and yang are the basic tenets of traditional Chinese medicine, yet when I am asked in clinic what they are I find myself fumbling to explain them. They are so basic and underlie almost everything I do, so much so that I don't often question how to describe them. I wanted to give an idea of what they are and an illustration of how they work together, especially since this time of year provides such a good example.At both their most simple and most complex, yin and yang are opposites. Everything and anything you can think of can be described as either very yin, very yang, or more commonly some degree of a mix between the two. Things which are more yin are hidden, darker, quieter, perhaps wetter. Yang types of things are bright, energetic, growing, moving, and changing. Yin is a feminine energy and yang is more masculine. Picture a hillside in the early morning: the side being warmed and brightened by the sun is more yang, and the side still dark and covered with dew is more yin.You never have yin or yang alone--they always work as a pair. Now, sometimes you'll have a situation where something is skewed so strongly in one direction or the other that imbalance starts to occur (and you need to visit your acupuncturist!). But one of the more interesting aspects of yin and yang is that at their extremes they begin to transform into one another. This can be explained using the example of the solstice.The winter solstice, which we will experience on December 21, is a time of ultimate yin. We are deepest into our journey away from the sun. The days are shortest and the night is longest. We're inspired to hibernate. But I always like to take note of the solstice because it is then, even if we can't sense it at first, that the days begin to lengthen toward spring. Like a pendulum beginning to swing in the opposite direction, yang is returning to our lives. I find it comforting to note the couple of extra minute of sunlight we begin to receive, even as it gets colder here in Chicago. If you're feeling the winter blues, I invite you to join me in finding and celebrating yang elements in this cold, yin-predominant season.