How do I know if a musical composition was originally written in A minor or in C mayor.?

Although they both have the same key signature, the two keys are not the same because the minor keys have a tendency to raise certain notes.

Imagine the piece is either written in C major or A minor, there are some things to look for that will help you figure out which key its in:

1. If you can play it, or have a recording of, what does it sound like? Happy?( major) or sad? ( minor)

2. what note does the melody start on? Is it C or G? ( notes of the tonic chord in C) or does it start on A ?

3. Look for specific raised notes:

The scale for C major is as follows

C D E F G A B C

with no accidentals

The natural minor scale for A minor is

A B C D E F G A

HOWEVER.

When composers write in a minor key, they often raise the " leading tone" so that there is a semitone relationship between the tonic and the note below it. In the case of A minor, A is the tonic and G is the subtonic ( literally "note below the tonic"), but if you raise it ( to G#) so that there is a semitone between the two notes, it will become the "leading tone".

In order to make a piece sound like its in A minor and not just in C, the composer will often use the notes of the harmonic minor scale, that is:

Harmonic minor scale

A B C D E F G# A

Sometimes they will use the notes of the Melodic minor scale

Melodic minor

A B C D E F# G# A

And as a result, you will probably see a bunch of G# ( and maybe a few F# )

When in doubt, the composer will often have written it in the score. Good luck!

Most classical works in a minor will have a g# leading tone. The best way is to analyze the harmony of the piece. If the cadences and tonal progressions resolve to a, then it's most likely in a minor. Fer Elise uses an E major chord as a dominant, which strongly suggests a minor. Also, only A natural minor is identical to C major. Melodic and harmonic minor, both more commonly used, have accidentals.

hope this helps

There are 2 quick and easy ways to distinguish relative major/minor from each other.

#1 Look at the first couple chords. Specifically look for chords that contain either A - C - E or C - E - G. Lots of A's signifies A minor. If you see any G-B-D, G Major chords, it's more likely C Major. Also look at the end to see what notes the piece ends on. The bass notes will be especially indicative here.

#2 Look for the leading tone of A minor. The leading tone of a minor key is the 7th scale degree raised a half step so that it is a half step down from the tonic. So that means to look for G#. G# will frequently appear in a piece that is in A minor, as will the dominant chord of A minor, E Major -> E G# B

The most accurate way is to ask the composer. Beethoven told us that piece is in A minor. Yeah, it sounds silly, but it's true.

If you don't have that info, you have to look at the tonal center and/or chord progression of the piece. Sometimes it takes a big handful of theory knowledge, but usually a piece starts and/or ends with the chord in the key in which it's written.

You can tell by the chordal structure used. In you're example, Fur Elise, the first arpeggio is on Am.