If I am composing a piece for 4 instruments and the 3 highest-pitched instruments already have formed a triad (therefore making the chord progression already), what should I have the bass part do? I usually have it jump back and forth reinforcing the notes of either the soprano or alto parts... Is there any strategy to using a bass instrument when a triad is already formed? Perhaps reinforcing the notes of the lead melody would be best? Or would it be best to make the bass reinforce the root of each chord?

Usually the bass note would reinforce the bass note of the chord. So the bottom note of the triad would work. But it really depends on the chord progression more than anything.

Yeah, just have the bass pulse out the root of the chord. That's a pretty easy technique that the best composers aren't too shy to use.

Well, if you can learn more harmony, you'd know the rules for doubling the notes. Example, if your song is in the key of C and you happen to be on the tonic chord, your triad is: C E G, but you can double either the C or G.

Sometimes, you don't have to double the notes of the triad. Try using appoggiaturas, passing notes, or pedal points, etc.

Ahh, I see what you mean, Alph. So I should basically just avoid using the third of each triad? Or is it just for C major?

A few questions:

*What's an appoggiatura? :P
*What's a pedal point? :P

Excuse my utter newbishness, but I've heard of these before but haven't ever understood what they are.

No no, for the tonic, you can double the root or the 5th, never the 3rd. I just used C as an example if it was the tonic. If A minor was the submediant for the key of C, then you may have the option of doubling the 3rd. Many more rules, etc.

Appoggiatura

Take one bar, 2/4 time signature, in the key of C major.

Soprano = high C
Alto = E
(these two notes are above middle C)

Tenor = G (in bass clef)

All three notes are half notes.

Bass: D (quarter note) moving to C (also a quarter note)

That D is an appogigatura. It doesn't belong to the C major chord. It is on the accented strong beat, and is temporary, being displaced by the C.

Pedal Point

Keep the bass as C.

Soprano, Alto, and Tenor may alternate between C and G chords. So, the C chord matches the C in the bass, but the G chord doesn't match the C in the bass, yet it still sounds okay. That C in the bass is the pedal point, because it's like the note C is being held by the pedal, figuratively speaking.