What Is a Chord? Guitar Chords & Theory, Explained
What a chord actually is, how chords are built from scales, the difference between major, minor, and diminished, how many chords exist, and how to play the dreaded Bm.
Ask ten guitarists “what is a chord?” and you’ll get ten answers, most of them either too vague or too theoretical. Here’s the clean one: a chord is three or more notes played together. That’s it. Everything else — major, minor, diminished, that Bm shape you’re dreading — is just which notes and why they sound the way they do. This is home turf for a chord library, so let’s actually explain it.
A chord is notes stacked together
Strum an open C major chord and you’re not playing one note — you’re playing several at once, and your ear blends them into a single sound with a “color” (bright, happy). Play A minor instead and the color turns wistful and sad. Same instrument, same strumming hand — the only thing that changed is which notes are sounding together. Understanding chords is really understanding which notes get along, and why.
Where chords come from: scales
Chords don’t appear from nowhere. They’re built from scales.
A scale is simply a set of notes in order, like a ladder of pitches that sound good together. The most important one is the major scale — the “do-re-mi” you already know. Here’s C major laid out on the neck:
To build a basic chord (a triad), you start on a note of the scale and stack every other note: the 1st, 3rd, and 5th. Do that from C and you get the notes C–E–G — which is exactly the C major chord above. That’s not a coincidence. The chords that sound “right” together in a song are the ones built from the same scale, which is why a key, its scale, and its chords are really three views of the same thing.
Major vs. minor: it’s all in the 3rd
The single most important interval in a chord is the 3rd, because it decides the mood:
- A major chord has a major 3rd → bright, resolved, happy.
- A minor chord lowers that 3rd by one fret (a “flat 3rd”) → darker, sadder, moodier.
That one-note change is the entire emotional difference between major and minor. Flip between C major and A minor and you can hear it instantly.
The common chord types
Beyond plain major and minor, a handful of chord “flavors” cover most music:
- Dominant 7th (e.g. C7) — major with a bluesy, restless edge; the engine of blues and rock.
- Major 7th (e.g. Cmaj7) — lush, dreamy, jazzy.
- Minor 7th (e.g. Am7) — smooth and mellow.
- Suspended (sus2 / sus4) — the 3rd is replaced, so they sound open and unresolved, itching to move.
- Diminished and augmented — the tense, unstable ones (more on diminished next).
What is a diminished chord?
A diminished chord takes a minor chord and also flattens the 5th — so it’s built from a root, a flat 3rd, and a flat 5th. The result is genuinely unstable and tense: spooky, suspenseful, like it desperately wants to resolve somewhere else. That’s exactly how it’s used — as a passing chord that creates tension before landing on a stable one. Here’s B diminished:
You won’t strum diminished chords around a campfire, but the moment you start writing your own progressions, they’re a powerful spice.
How many guitar chords are there?
Technically? An enormous number. You have 12 possible root notes, a dozen-plus chord qualities for each, and then multiple shapes (voicings) to play each one in different spots on the neck. Count all the voicings and you’re well into the hundreds — this site’s library alone holds nearly 200 chord pages.
But here’s the reassuring truth: you only need about eight chords to play thousands of songs. The giant catalog is there for when you’re curious or writing music, not a list you have to memorize. Browse the full chord library when a song calls for a shape you don’t know yet.
How to play Bm (the beginner’s rite of passage)
Almost every beginner hits a wall at B minor, because it’s usually the first barre chord — you lay one finger flat across all the strings like a movable “nut,” then build a shape on top. Here it is:
Three tips that actually help:
- Roll your barre finger slightly onto its bony side rather than pressing with the flat, soft pad — it fingers cleaner with less effort.
- Keep that finger close to the fret and your thumb low on the back of the neck.
- Build strength gradually. Nobody nails their first barre chord; it takes a couple of weeks of daily tries. When it clicks, a whole world of movable chords opens up.
So what’s a riff, then?
People mix up chords and riffs, so let’s settle it. A riff is a short, repeated musical phrase — a hook — and it’s usually made of single notes or power chords, not full strummed chords. Think of the most famous guitar moments you know: those instantly-recognizable opening figures are riffs.
In rock and metal, riffs lean heavily on power chords — just the root and 5th, no 3rd, so they’re neither major nor minor, just pure and punchy under distortion:
Riffs also borrow heavily from scales — the minor pentatonic is the riff-and-solo workhorse of rock and blues. So chords, scales, and riffs aren’t separate worlds; they’re the same notes used three different ways.
Tools to explore chords
This is where a chord library earns its keep:
- Found a chord shape in a song and don’t know its name? The chord identifier tells you what chord it is from the frets you enter — reverse-engineering at your fingertips.
- Want to hear how chords flow into one another? The chord progression generator plays sequences back at any tempo so you can feel why some chords resolve and others create tension.
- Just want to learn shapes? The full library has every chord with diagrams and audio.
Where to go next
Now that you know what a chord is, learn to read the diagrams and tabs that show them in how to read guitar tabs, or step back to the complete beginner’s guide to see where chords fit in the bigger picture. The theory is genuinely fun once it starts clicking — and it clicks fastest when you play the chords while you read about them.