A guitar player once told me a capot (capo?) cannot be used on a banjo. But, why not? Physics is physics. Wouldn’t it work the same on a banjo?
It’s “capo.” Here’s a YouTube video:
I’m a banjo player, so I’ll chime in. I play with a capo all the time. Most banjos, however, are the five-string kind, with the top string being five frets shorter, so a capo placed on one of the first four frets will only get the lower four strings (and it’s always on one of the first four frets).
To get around this, you can just tune the fifth string a little higher (but not too much, it weakens the steel string), or you can do some tricks to capo the fifth string. I’ve installed railroad spikes on my banjos. I bought little tiny railroad spikes made for model railroads (can’t recall the gauge), and you glue them in just below the fifth string, right between two frets, so that there’s room to hook the fifth string under the angle part of the railroad spike. I have my banjos spiked two, four, and five frets up on the fifth string.
He must not have actually spent any time around banjo players - they certainly can be, and frequently are.
I love this. Great explanation and love the thought of spiking the Fifth string.
I must admit: I tend to never use a capo. It is a combination of stunning laziness - simply can’t be bothered; and an unsubstantiated bias I have: I feel like a capo changes the overall feel of playing that guitar. Changes the “real estate” I have to work with.
My pro friends use capos constantly, to revoice their guitar to pair it with another player, or adjust the key to their voice. But not with Bluegrass - ya play that in G, son! My '48 Martin D-18: I feel pretty comfortable saying you can tell this guitar has had a G chord played on it a lot. The grip is just right and the chord just pops on that guitar. I haven’t played it with a banjo; I should.
Fun discussion. I’m just the bass player, but I occasionally listen in on what the real musicians (and the banjoists!;)) say. One of our guys (banjo/fiddle) is a pretty accomplished luthier, and he has spiked several other pickers’ banjos.
I recall a similar discussion a couple of months back where folk mentioned some guitarists who refused to capo, up against session pros who never gave it a second thought. Never mind me - I’ll just keep thumping away over here in the corner, trying to rememeber that that capoed D chord I’m looking at isn’t really a D…
Guitar players often take some pride in being able to play in any key without a capo, and I can understand that if you’re good enough.
There’s a physics reason that a banjo is treated differently. The bridge, being mounted on a drum head, transfers its vibration energy to the air much more quickly than a guitar does, with the bridge mounted on a relatively stiff piece of wood. Because of that, a banjo is louder, but has much less sustain that a guitar. Since it has hardly any sustain, you have to play it fast, staccato. Since you have to play it fast, you have to depend on a lot of open strings, thus the open-chord tuning. And because of that, you have to capo to play a different key.
By the way, a lot of bluegrass/folk is in G, but not all - a lot of fiddle tunes are in A.
I’m not very good, but a couple of songs I’ve been playing lately require some capoing. Mumford & Sons’ I Will Wait was recorded in D-flat, with the banjo tuned down one fret. I play it in D, with the lower four strings tuned normally, and the shorter fifth string capo’d up two frets to A.
I Am a Man of Constant Sorrow from the Soggy Bottom Boys is in F, and the banjo part is played with the lower four strings capo’d up three frets, and the fifth string capo’d up five frets (so it’s at the tenth fingerboard fret).
So: why the heck don’t you post more often on music/stringed instrument threads? Nice post. Yep, I get the LOUD and brief shape of banjo notes, but hadn’t fully connected that to the Open tuning. Good stuff. Funny, I built a cigar-box guitar with my son a few years ago and we tuned it to Open G but I hadn’t connected that - it was as much because an Open tuning is a bit more…forgiving 
As a fellow bass player, amen to the bolded part.
I always thought that the main reason for a capo on a guitar was so that open chords could be played in a wider variety of keys.
I referred to that as “lining up with the vocal.”
Another reason is be able to play chords that complement other players. If someone plays an open G, another guitarist can capo at the 5th fret and play a D chord, and get a voicing of G that is different-but-fits with that other guitar’s G. And the D player now has access to other classic D arpeggio licks to weave in, now in G and working with the other guitarist really well.
Does that help?
One night, I was messing around trying to learn intro guitar part “Hotel California” which involves putting a capo on the seventh fret. I didn’t really accomplish my goal, but in my noodling a came up with what I think is a really nice set of chord changes. I took the capo off thinking that surely if it sounds good way up on the neck, it will sound amazing with ringing open position chords.
Nope. I’ve since tried it on each fret I-VII. It’s the same shapes and intervals, but the only place it sounds “right” is on the seventh. It’s weird. Each position seems to have its own character.