Beauty is the phenomenon of the experience of pleasure, through the perception of balance and proportion of stimulus. It involves the cognition of a balanced form and structure that elicites attraction and appeal towards a person, animal, inanimate object, scene, music, idea, etc.
Understanding the nature and meaning of beauty is one of the key themes in the philosophical discipline known as aesthetics.
The composer and critic Robert Schumann distinguished between two kinds of beauty, natural beauty and poetic beauty: the former being found in the contemplation of nature, the latter in man's conscious, creative intervention into nature. Schumann indicated that in music, or other art, both kinds of beauty appear, but the former is only sensual delight, while the latter begins where the former leaves off.
A common theory says that beauty is the appearance of things and people that are good. This has many supporting examples. Most people judge physically attractive human beings to be good, both physically and on deeper levels.
"Beauty as goodness" still has whole classes of significant counterexamples with no agreed solution. These include such things as a glacier, or a ruggedly dry desert mountain range. Many people find beauty in hostile nature, but this seems bad, or at least unrelated to any sense of goodness. Another type of counterexample are comic or sarcastic works of art, which can be good, but are rarely beautiful.
It is well known that people's skills develop and change their sense of beauty. Carpenters may view an out-of-true building as ugly, and many master carpenters can see out-of-true angles as small as half a degree. Many musicians can likewise hear as dissonant a tone that's high or low by as little as two percent of the distance to the next note. Most people have similar aesthetics about the work or hobbies they've mastered.
