http://www.sacred-texts.com/eso/sta/sta19.htm
While the early Chinese, Hindus, Persians, Egyptians, Israelites, and Greeks employed both vocal and instrumental music in their religious ceremonials, also to complement their poetry and drama, it remained for Pythagoras to raise the art to its true dignity by demonstrating its mathematical foundation. Although it is said that he himself was not a musician, Pythagoras is now generally credited with the discovery of the diatonic scale. Having first learned the divine theory of music from the priests of the various Mysteries into which he had been accepted, Pythagoras pondered for several years upon the laws governing consonance and dissonance. How he actually solved the problem is unknown, but the following explanation has been invented.

Pythagoras pondered for several years upon the laws governing consonance and dissonance. How he actually solved the problem is unknown, but the following explanation has been invented.


arbitrary
adj arbitrary [ˈaːbitrəri]
"not decided by rules or laws" but by a person's own opinion He made a rather arbitrary decision to close the local cinema without consulting other people.
adv arbitrarily

Pythagoras pondered for several years upon the "laws governing consonance and dissonance." How he actually solved the problem is unknown, but the following explanation has been invented.

IRONIC

I don't like red text or ironic shouting.
Please scale it down.


As for the OP's question, the real answer is because we are animals who like order and safety. Some of us flirt for a while with danger and atonality because it gives us cheap thrills and makes us feel different, but deep down we all desire the fundamental things in life that we associate with a steady home.
Even more so if you were raised by wolves, like me.

Interesting that you would quote the most limited meaning provided by a page of several sets, the one explicitly marked as a translation rather than a definition.

Did you miss this more complete one, also at the same obvious first link given by google? (freedictionary.com)

Pretty much a cultural thing. You get used to a certain range of pattern and anyone else who stumbles upon that pattern call it Mid-East music or something else...

Historically the origin of the major/minor system is to seek in the "rule of the octave" circa 1600.


http://faculty-web.at.northwestern.edu/music/gjerdingen/part imenti/aboutParti/ruleOfTheOctave.htm

Check out this book if you are interested in the subject: "Principes de l'accompagnement du clavecin" of Jean-François Dandrieu, 1690. This is the easy way, no real shortcut though, starting from scratch it will take you about 2 or 3 months to master, sort of.

http://imslp.org/wiki/Principes_de_l%27accompaignement_du_cl avecin_%28Dandrieu,_Jean-Fran%C3%A7ois%29

Most practical music though does not use all these mathematically pure ratios. In equal temperament for example, according to you, we should perceive major thirds as highly dissonant!

(Though note that both scales and basic "tonality" predated the universal adoption of equal temperament and the pitch standardisation of A=440Hz by several centuries).

As I said before, the OP question was the musical equivalent of asking "What is the meaning of life?" - This thread could go on for pages and still not get anywhere close to giving a satisfactory answer.

To write a scale such as C Major (in the case of a piano or midi keyboard)we implement what is known as the chromatic scale. As you would probably find in any music theory book a musical scale is " a rising or falling of notes that occur within the range of an octave and carry on in the other octaves" These notes are then selected from a scale for the purpose of melody and harmony (Consonance). The point is that knowing these scales lets you identify which notes will work best together and you wont end up writing or playing "bum notes",
also each scale has a particular musical sense and feel to it which is why most western music is written in certain scales, such as C Major. Major scales and chords are associated with brightness and happiness, where as the minor chords are associated with deep melodies and have a kind of darker mood and feel to them. When I first started writing music I didn't use any scale, I would compose and listen to the melody and chords as I played to reflect upon the mood that I felt inside, given shape and form externally in the music. The music wasn't written in any scale, not that I knew of, But that doesn't stop the fact that the music I wrote would have been governed by a certain musical scale if i would have looked it up.
The octaves of a keyboard are made up of notes, 12, 5 black and 7 white, and this is where the purpose of the Key signature applies to the scale. Any of these keys can be the beginning of a musical scale. A scale that begins with the note C as its beginning is said "To Be in the KEY of C".
The scale of C major is the easiest of the scales to learn as its 7 notes are the 7 white keys C,D,E,F,G,A,B on the keyboard. Learn to familiarize yourself with the scale by playing the keys up and down, this way you will be able to identify with its sound and feel in your mind. Basically the octave is split into 12 intervals, or 12 semitones, an interval is a the gap between each note. The series of semitones are defined by a scale of pitches, which are known as the CHROMATIC SCALE. The chromatic scale is not particularly used as a musical scale, but features the notes from which other musical scales feature, and may be selected. The C major scale uses 7 of the notes, the 7 white keys, the black keys do not have place in the key of C major, they are not needed. In order to write a scale you need to associate with the way that the semitones and tones are set in order,(order of the chromatic scale),
TONE,TONE,SEMITONE,TONE,TONE,TONE,SEMITONE.
Every white key which has a black key next to it is a full tone apart from the next white key. A white key that is next to another white key is a SEMITONE APART- E TO F AND B TO C. You simply need to recognize these patterns in order to write your own musical scale.
You will choose your root note, for instance, D and then follow the above chromatic scale to find the musical scale of that Key.
Its a little complex to start with, but with a little learning you should soon get it. The thing to remember is the 12 keys that are each a semitone, and then apply the following TONE,TONE,SEMITONE,TONE,TONE,TONE,SEMITONE to get to know the various musical scales. This only deals with Major and Minor chords,
minor chords start in the black notes and follow the same chromatic scale to work out how that particular musical scale works. The fact is there are a lot of musical scales to choose from such as the pentatonic scale, microtonal scales, octatonic and hexatonic scales. This post is way too long and and I have even tried my hardest to put it in the shortest way that i could. By now you should be realizing the magnitude of the question you asked. If you really mean business then you should either get a proper musical theory course or plenty of books to read. I am only just beginning to learn these things myself.
No doubt Ill get told I'm wrong and whatever but this should give you a good head start into what your'e wanting to know. I learned some musical theory after reaching a point where i needed to expand my knowledge of the subject. It was well worth it. It seems not long back i was asking the very same question at the top of the page.
Trakstar

PS._black keys are referred to as flat if they occur at the left of a white note,(because they are flatter in pitch) and sharp if they occur at the right of a white key(because they are sharper in pitch). Thats it for this post-time for a vacation me thinks. Goodbye

The OP asks: "We have scales but why??"

The obvious answer is: "Because!"

The same goes for questions like: We have front and back, up and down but why? We have past and future but why? We have good and bad, true and false but why?

Because: 1. This is how the universe is structured, and/or 2. This is how our brains are structured. And there is nothing arbitrary about either.

The least we could say (and some posters have said it above), is that our minds tend to find ever more complicated patterns wherever they look. Intelligent design? Who knows...

Thank you so very very much

+1000

Shouldn't this thread have a poll with a fish option?

that's half of the story.

we perceive simple ratios as more consonant only because our typical western instruments have partials that follow (approximately) a harmonic series - i.e. the frequencies are integer multiples of some fundamental. this leads to the fact that simple ratios between two tones (each with its own harmonic series) produce less beating between partials than with more complex frequency-ratios. in other cultures - where other instruments (like percussions, with non-harmonic partials) dominate, other scales are used. there's interaction between timbre and scale. with a properly chosen timbre, you can make even the octave sound dissonant - or whatever interval of your choice consonant. see here:

http://sethares.engr.wisc.edu/consemi.html

fascinating stuff. i'd say, nothing short of some grand unifying theory for consonance.

humans like to think chaos can be ordered.

and get far too stressed when things don't fit into nice neat little boxes with clear labels on them