How to differentiate between relative keys?

Question

So I'm learning that C major and A minor scales have the same notes. Then, if I look at, say, 10 consecutive single notes, how do I tell if they're in C or Am? It's easier when you see a chord, since you can count the semitones between the notes and deduce if it's major or minor (not sure if what I'm saying is technically correct), but when you see consecutive single notes, how do you differentiate between the major key and the relative minor key? If you play the scale from root note to root note, you can differentiate, but if you play some sequence, is there any pattern to look for that tells you it's C or Am?

Answer 1

If you're looking at a bunch of consecutive notes, you're probably looking at a melody. If you're looking at a melody, it probably ends (and more than likely begins) with the tonic note of the scale—C, in the case of C major, or A, in the case of A minor.

There are other defining features of a given key—the 5th note of a scale is usually very important, for instance. So if G is the highest note in the melody, or repeated a lot, it's much more likely C major than A minor.

Also, minor keys usually have their 7th scale degree raised by half a step—you'll very often see G-sharp in A minor, whereas you'll much more rarely see it in C major.

Once you start looking at chords rather than just individual notes, there are more ways to tell. But this is a start.

Answer 2

I agree with David W's answer. Almost all the time, a complete melody will end on the 'home note' (which is the key of the piece). In this instance, a tune that's in A minor (no sharps or flats in the key signature) is very likely to end on A. But there are other ways to tell the key of a piece, if you're sensitive to them. One is the feeling of the music: if it feels basically bright and happy, it's probably in major, tho there are exceptions, such as Hava Nagila, which is entirely in minor, or Irving Berlin's "Blue Skies," which begins in D minor and ends in F major (D minor's relative major, as D minor and F major share the same key signature). And if it feels dark, mysterious or sad, it's likely in a minor key - e.g. Mendelssohn's Hebrides Overture.