Anyone who has walked down the shady side of a street on a summer\'s day, found it a bit chilly, and thought to themselves to cross over to the sunny side of the street to enjoy the warmth of the sun has, whether they realise it or not, made a transition from yin to yang. Similarly anyone who has found the sun too intense, too glaring, too sweltering and no longer pleasant to be in and has sought the shade has seen the benefit of a change to yin when yang has become too overbearing.

Yin and yang are polar opposites used in Chinese philosophy as an overlay on the world, two pigeon holes into which are sorted, respectively, dark and light, cold and warm, shady and sunny, wet and dry, empty and full, female and male, passive and active, and numerous other divisions. Originally the character yin referred to the shady side of a mountain and yang to the sunny side. In my view the yin and yang sides are best seen as changing with the position of the sun, rather than as fixed attributes of specific sides. However, just so as I don\'t confuse you when you read books on this that trot out the standard definitions, let me add that yin was originally regarded as the north side of a mountain and yang the south side. This of course says nothing about the relative sunniness and shadiness of the eastern and western slopes as the sun moves east to west during the day, and takes little account of the angle of declination of the \'south\' side, i.e. how many degrees east or west of due south it actually is. But any gardener knows the benefits of a south-facing wall and unless they want a wall-mounted sundial on it \'roughly south\' is good enough. This is the same kind of rule of thumb being applied when seeing the yang side of a mountain as the south side. It is important to remember though what makes the south side of the mountain yang, its relative sunniness, and so a more fluid appreciation is that the sunny side at any particular time is the yang side, regardless of direction. This appreciation preserves a sense of yin and yang changing into each other. As I write this, in the afternoon, the eastern side of my street is sunny and the western side in shade. But early in the morning it was the other way around. [Page]