If you go for cliches, the beauty is in the eye of the beholder but if you dig the philosophic stuff, an Aristotelian beauty is a thing of practical nature--something useful. It has bothered me a lot why beauty is so popular because this requires me to understand what the beauty really is. I have done my bit here by analyzing why beauty is popular and how to appreciate beauty.
Beauty is, if I can be frank, something appreciated; the artist can create the best canvass but if no one appreciates it, it is not beautiful. Why do then some things appreciated more than others. Why for example, a beautiful woman like Yasmin Ghauri whose picture is given here with her permission; a fashion model, she is beautiful, she thinks so and so do many people but what is special about her? Nothing except millions would crave for her. Nature has dowsed our brain with accepting things that are good for Nature, not for us. And that is the name of a game called procreation. Women of certain body shape are considered more suitable for procreation and Nature makes us love them so that we can perpetuate the traits that make our genes stronger. However, this theory appears to fail when we look at beautiful buildings. Not all beautiful buildings are practical or even serve any purpose. Take for example, Taj Mahal, a giant monument to love but was it necessary to build this wasteful structure? The reason why it is considered beautiful lies in its creativity, as would be the case for Picasso's canvases. Creative minds are considered necessary in any society and thus society places great emphasis on calling it beautiful. Again, if you look at the bigger picture, it is an attempt by Nature to preserve our race. What a plan? What a slavery?