George Santayana in “The Sense of Beauty”
Beauty is pleasure regarded to the quality of thing. Beauty is a value, that is, it is not a perception of a matter of fact or of a relation, it is an emotion, an affection of our volitional and appreciative nature. An object cannot be beautiful if it can give pleasure to nobody. A beauty to which all men were forever indifferent is an contradiction in term
In the second place this value is positive, it is the sense of the presence of something good, or (in the case of ugliness) of its absence. It is never the perception of a positive evil, it is never a negative value. That we are endowed with the sense of beauty is a pure gain which brings no evil with it. When the ugly ceases to be amusing or merely uninteresting and becomes disgusting, it becomes indeed a positive evil: but a moral and practical, not an aesthetic one. In aesthetics that saying is true — often so disingenuous in ethics — that evil is nothing but the absence of good: for even the tedium and vulgarity of an existence without beauty is not itself ugly so much as lamentable and degrading. The absence of aesthetic goods is a moral evil: the aesthetic evil is merely relative, and means less of aesthetic good than was expected at the place and time. No form in itself gives pain, although some forms give pain by causing a shock of surprise even when they are really beautiful: as if a mother found a fine bull pup in her child's cradle, when her pain would not be aesthetic in its nature.
Further, this pleasure must not be in the consequence of the utility of the object or event, but in its immediate perception; in other words, beauty is an ultimate good, something that gives satisfaction to a natural function, to some fundamental need or capacity of our minds. Beauty is therefore a positive value that is intrinsic; it is a pleasure. These two circumstances sufficiently separate the sphere of aesthetics from that of ethics. Moral values are generally negative, and always remote. Morality has to do with the avoidance of evil and the pursuit of good: aesthetics only with enjoyment.
Finally, the pleasures of sense are distinguished from the perception of beauty, as sensation in general is distinguished from perception; by the objectification of the elements and their appearance as qualities rather of things than of consciousness. The passage from sensation to perception is gradual, and the path may be sometimes retraced: so it is with beauty and the pleasures of sensation. There is no sharp line between them, but it depends upon the degree of objectivity my feeling has attained at the moment whether I say "It pleases me," or "It is beautiful." If I am self-conscious and critical, I shall probably use, one phrase; if I am impulsive and susceptible, the other. The more remote, interwoven, and inextricable the pleasure is, the more objective it will appear; and the union of two pleasures often makes one beauty. In Shakespeare's LIVth sonnet are these words:
     O how much more doth beauty beauteous seem
     By that sweet ornament which truth doth give!
     The rose looks fair, but fairer we it deem
     For that sweet odour which doth in it live.
     The canker-blooms have full as deep a dye
     As the perfumed tincture of the roses,
     Hang on such thorns, and play as wantonly
     When summer's breath their masked buds discloses.
     But, for their beauty only is their show,
     They live unwooed and unrespected fade;
     Die to themselves. Sweet roses do not so:
     Of their sweet deaths are sweetest odours made.
One added ornament, we see, turns the deep dye, which was but show and mere sensation before, into an element of beauty and reality, and as truth is here the co-operation of perceptions, so beauty is the co-operation of pleasures. If colour, form, and motion are hardly beautiful without the sweetness of the odour, how much more necessary would they be for the sweetness itself to become a beauty! If we had the perfume in a flask, no one would think of calling it beautiful: it would give us too detached and controllable a sensation. There would be no object in which it could be easily incorporated. But let it float from the garden, and it will add another sensuous charm to objects simultaneously recognized, and help to make them beautiful. Thus beauty is constituted by the objectification of pleasure. It is pleasure objectified.
Plato about beauty
Plato was in great interest in trying to pin point the role of beauty in society. Plato believed, among other things that relative beauty only exists when you compare objects to each other. If some aspect of an object is beautiful, the whole object is beautiful. After further consideration, Plato came up the most logical of all the philosophies, that beauty cannot be defined. Some things have the "ideal beauty" and no one can consider it not beautiful. It is also in agreement of Plato throughout time that beauty provokes pleasure. Following in the ideas of Plato, Plotinus also preached that there is no one object that beauty can be defined as nor is there one aspect of any object that beauty can be defined as. He also believed that "beauty is that which irradiates symmetry rather than symmetry itself." Plato created a trend in that beauty cannot be defined, yet philosophers continued to struggle with the meaning. Aristotle hypothesized that the senses most prone to recognizing beauty are sight and hearing.
My opinion about beauty
It's quite hard to define what is beauty. The beauty is abstract. The beauty is real and we can really feel it if it is related to something concrete or the work. In other word we can enjoy the beauty if it's related to a concrete thing. Beauty can be felt by the concrete thing. So It's hard to define the beauty, but it is obviously for us to define something beautiful. Beauty is just a concept that can be felt if it has form, for example : song, body shape, film, landscapes, music, decoration, person, painting etc.
It must be differed the beauty as something abstract and as the something beautiful. Beauty has a wide meaning. It includes
The beauty of art
The beauty of nature
The beauty of moral
The beauty of intellectual
The pure beauty is something which is experienced by human in conjunction with something absorbed by them. Beauty also has the limited meaning. It is something which can be absorbed by sense of sight, for example the beauty of form and colour.
That explanation and the division above is still unclear about what truly beauty is. One of the way to know the answer is looking for the general specification in something (regarded as) beautiful and compare it to specification in the meaning of beauty. Therefore the beauty itself actually is a certain value which exists in a thing. The quality of the value itself usually is called the unity, balance, symmetry, and harmony.
From that specification, we can conclude that beauty is constructed from harmony, symmetry line, colour, form, sound and words. In my opinion beauty is a unity of the harmony relations in a thing.
Beauty is a unity of harmony relations of our sense perception. Beauty can be related to the idea of a pleasure which is something enjoyable for our sense. Beauty is something pleasure if it's seen, heard, felt by our sense. People prefer to define and feel something beautiful rather than the beauty which is abstract. Because something which can be observed, analyzed and defined is something concrete.
The beauty is value which can be differed between subjective value and objective value. Subjective value is value which is judged based on the subject/the creator of the thing. And objective value is value judged based on knowledge or scientific method. Beauty is also differed to the value of personal and the value of society. The value of personal is value judged by personal perception. And the value of society is based on a certain society perspective. But the important thing to manage is extrinsic value and intrinsic value. The extrinsic value is a quality of the thing as the media to something else (instrumental or contributory value). It is a value which is as the tool, the purpose or it is for the interest of that thing itself for example : a poem consists of language, verse, diction, rhythm. These are the extrinsic value and the message which is conveyed in the poem is intrinsic value
Source :
The Sense of beauty, page 49-52
http://ablemedia.com/ctcweb/showcase/greenwaldgreece3.html