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What is a triad?
Defining a triad can kind of depend on context. Without any specific context in mind you can argue a triad is when you build a harmony of three different tones. That’s not a be all end all exclamation though. While it is fundamentally accurate, over time music theory has adopted certain contexts where defining a triad becomes a lot more narrowed down.
In short the rule of thumb is when someone brings up triads they’re talking about harmonies based around stacked 3rds. To put it more simplistically from the root you go up a 3rd (major or minor), then from there you go up another 3rd (again, major or minor).
The most common definition you’ll get for a triad is the four triads. Major, minor, augmented, and diminished. The intervals they are made up from can be lumped into two categories based off the first 3rd. That gives us major triads and minor triads.
Major: Tonic, major 3rd, perfect 5th
The major triad is built from any starting tone and goes up a major 3rd, and from the major 3rd goes up a minor 3rd. Enter the major chord. Bright sound.
Minor: Tonic, minor 3rd, perfect 5th
The minor triad pretty much reverses the roles of the two types of 3rds. From any tone you go up a minor 3rd, then up a major 3rd. Better known as the minor chord. Gloomier sound.
Augmented: Tonic, major 3rd, augmented 5th
The augmented triad from the start goes up a major 3rd, and from there up another major 3rd. I’m still not sure how to describe how it sounds. The two major 3rds have a brighter sound, but from the tonic to the second major 3rd is a minor 6th and that contrasts the brightness a bit. I’ve never landed on a description that I’ve felt appropriately describes it, so I usually just say it sounds weird.
Diminished: Tonic, minor 3rd, diminished 5th
The diminished triad from the starting tone goes up a minor 3rd, then up another minor 3rd. The distance from the tonic up to the second minor 3rd is a diminished 5th, and naturally this is one of the tenser harmonies you can bend to your will. Dark sound.
The major, minor, and diminished are all native to the major scale in that if you follow the premise listed above you’ll be able to form those three triads. The augmented triad you have to fidget with other scales to be able to get it naturally. Or you can just use it for the hell of it because you know how to put one together and you don’t really need any other reason.
For the time being I’m going to leave building triads at that, but suffice to say there are other approaches to the same thing that offer different perspectives. I’ll get into those at a later date so in the meantime siphon this from your monitor as though it were the radiant light of awesome I shoot from my chest.