So, typically you compose a happy song in a major scale, or, in my case Progressive House, in a Major scale.
But, if C# major's relative key is A# Minor, what exactly is a major scale and how do you compose a song in a major scale?
Have I misunderstood something and maybe you have to write a happy song in MAJOR CHORDS, or what?
C# major's relative minor key is A# Minor. These two keys both contain the same notes but a different tonic (in this case the tonic being C# and A#, accordingly)
C♯(i) D♯ E♯ F♯(iv) G♯(v) A♯ B♯
A♯(i) B♯ C♯ D♯(iv) E♯(v) F♯ G♯
This doesn't really have any bearing on how you write a song in a major key, but it does help us to understand the relationship between them.
To put it very simplistically, to write a general "pop" song in C# major you will root your melody (riffs and hooks) and harmony (chord changes) around the C#. This is usually manifest in starting and ending on the I (home) chord of C#maj, with support from the IV and V chords of F#maj and G#maj. This should sound kinda happy.
To write in A# Minor you use all the same chords and notes, but rooted around the A#. So try starting on the I (home) chord of A#min, with support from the IV and V chords D#min and E#min. This will sound kinda sad.
Once this basic idea starts to make sense, throw some extra chords in to each framework, remembering to anchor around the I, IV, and V.
C#maj(i) D#min E#min F#maj(iv) G#maj(v) A#min B#dim
A#min(i) B#dim C#maj D#min(iv) E#min(v) F#maj G#maj
This is a very simplistic explanation which I'm sure will not hold up to any great scrutiny, but I offer it up as a basic answer. Full disclosure, I'm not a trained musician, this is how I understand these things to hang together.
Something that's related to your question is the mode theory. Here's a nice article on that! It boils down to:
> If you play your scale (e.g. C major [C D E F G A B]) on a set of chords
with a tonal centre of C major, and you focus on the relative position of the notes
towards the C in the scale, it will sound happy (Ionian)
> If you play your scale (e.g. C major [C D E F G A B]) on a set of chords
with a tonal centre of A minor, and you focus on the relative position of the notes
towards the A in your scale, it will sound sad (Aeolian)
So for a 'happy' song, you can also add minor chords, but be sure to construct them around a tonic centre of a major chord. Of course, in the end, it also comes down to personal preference where some people find that minor chords can also sound happy - as Caleb pointed out in the comments. It also depends a lot on which notes of the scale you're most focusing on. If you target the specific minor notes the most, then of course it will sound more 'minor'/sad in general. If you want your specific song in C#major to sound very happy, maybe try to focus on the major 3rd of the chord (F) and see what that produces.
This can also be an interesting read.
Scales are in essence a series of notes a certain amount of intervals / semitones from each other. You can have the semitones in any place in the scale. You can have various amount of notes in the scale. 8 notes in the scale is common as it represents all the scale degrees.
Major Scales have the semitones between the third and fourth scale degrees and the seventh and eight scale degrees. You can start on any note in the chromatic scale and play 8 notes from that note and as long as you have 8 notes and the semitones at those places you will have a Major scale of some sort.
Do you know what a half-step and a whole step is? Start on any note on any western tonal instrument and follow this sequence:
whole -> whole -> half -> whole -> whole -> whole -> half
You've just played a major scale. The name of the note you started on is the name of the key you're in. If you follow that pattern of whole and half steps you will always get a major scale.
Play it a few times. Give each note a number: 1 -> 2 -> 3 -> 4 -> 5-> 6 -> 7
Start on note # 6 and follow this sequence of whole/half steps:
whole -> half -> whole -> whole -> half -> whole -> whole
If you did it correctly you just played a minor scale. This is the major scales 'relative' minor (they have the same notes) Notice where the half steps occur in the major scale vs the minor scale.
Might be a good place to start..
In my own experience, I used to think that in order to compose a happy tune, one must stay away from minor chords. This is NOT the case at all. The diatonic 6 chord (in c major, scale degree 6 is pitch A.) One can construct the diatonic chord (a chord that uses only notes that belong to the key one is using) with 'A' as the root (the pitch on which the chord is built) A-C-E . This minor chord will not necessarily make one's music sound sad. Rather, it will serve as a sort of a transition between the more important chords of the key. Listen to Pachabel's Canon In D ]and listen for the "sad" chords: b minor, and F# minor. Also keep in mind that it is common practice to begin and end on the major tonic chord, however this is not always the case depending on the type of music one is writing. Music in a minor (sad, gloomy, mysterious) key can still have an overall effect of being happy. Brahms' Hungarian Dance no. 5 is one of many examples as for its dance quality.
