What is a chord? Multiple notes sounded at the same time. Many definitions would insist on three or more notes and call a combination of two notes a dyad… but other definitions call a dyad a two-note chord. Taken on its own, a pair of notes is open to a lot of interpretations. Adding more notes often makes it clearer what a chord should be called although you still need to consider the context.

There are limits on how many notes you can include before the waters start to become muddier rather than clearer. Mash down all the notes you can fit under your fingers on a piano keyboard and it isn’t so much a chord as a cacophony. The latter description often also applies to playing a smaller group of notes very close to each other although, if you lift some of them up or down an octave, a meaningful pattern may emerge.

Assuming a solo instrument, different possibilities present themselves. On a piano, you can play tighter clusters than on most stringed instruments. However, you can only play each individual note once while something like a guitar or bass can play the same note twice (more with some techniques). The choice of how to play a chord can be dictated by many different things. For a beginner, it is probably the one shape they have learned for the chord. A more advanced player will realise that there are multiple options and they might pick in order to emphasise a line flowing through a series of chords, or based on genre or other stylistic considerations (or they might be reading music which dictates or suggests a particular combination.

Even when the same note can be played more than once, each instance of the note will have a different timbre in most tunings, affected by the length and mass of the vibrating portion of the string and how it was struck. Timbre is created by how a given note contains combinations of multiples of the fundamental frequency. An A at 110Hz will also contain some measure of 220Hz, 330Hz, 440Hz and more. That 330Hz is an odd one out in that group – all the others would be heard as an A if isolated but the 330Hz is just a hair sharper than an E (329Hz), so even a single note with all but the purest toned instruments contains harmonic content hinting at chords, and that can be another (often unconscious) factor in which combinations of notes are selected.

Is that everything I know about chords? Probably not, but I thought I’d try a quick brain dump on the topic and see what came to mind. What got me started? Figuring out what chord shapes I was going to use on ukulele today for a song I was leading for the toddlers’ group at church and trying to remember how to play a B7 (like a simple Em but moved across one string – 4 3 2 0 or B4 D#4 F#4 A4 in finger position or note terms). Sounds lovely in the context I needed it for, next to my basic Em (0 4 3 2 / G4 E4 G4 B4).