(Got this from the Old Time Music in Rhode Island Facebook page. Says on there that it was passed on from Michael Pavan).
Old Time and Celtic songs are about whiskey, food and struggle. Bluegrass songs are about God, mother and the girl who did me wrong. If the girl isn't dead by the third verse, it ain't Bluegrass. If everyone dies, it is Celtic. Old Time and Celtic bands have nonsense names like 'Flogging Molly' 'Fruit Jar Drinkers' and 'Skillet Lickers' while Bluegrass bands have serious gender-specific name like 'Bluegrass Boys,' 'Clinch Mountain Boys' and 'Backwoods Babes'. The most common Old Time keys are major and minor with only 5 notes (modal). Bluegrass uses these, plus Mixolydian and Dorian modes, and a Celtic band adds Lydian and Phrygian modes. A Bluegrass band has between 1 and 3 singers who are singing about an octave above their natural vocal range. Some Old Time and Celtic bands have no singers at all. If a Celtic band has a singer, it is usually either 1. a bewhiskered ex sailor, or 2. a petite soprano. A Bluegrass band has a vocal orchestrator who arranges three part harmonies. In an Old Time band, anyone who feels like it can sing or make comments during the performance. In a Celtic band, anyone who speaks during a performance gets 'the look', and songs are preceded a call for silence and a detailed explanation of their cultural significance. Bluegrass tunes & songs last 3 minutes. Old Time and Celtic tunes & songs can be any length, and sometimes last all night.
A Celtic banjo is small and quiet. An Old Time banjo is open-backed, with an old towel (probably never washed) stuffed in the back to dampen sound. A Bluegrass banjo has a resonator to make it louder. A Celtic banjo weighs 4 pounds, an Old Time banjo weighs 5 pounds, towel included and a Bluegrass banjo weighs 40 pounds. A Bluegrass banjo player has had spinal fusion surgery on all his vertebrae, and therefore stands very straight. If an Old Time banjo player stands, he slouches. A Celtic banjo player remains seated to maintain stability while cross-picking as fast as possible. An Old Time banjo player can lose 3 right-hand fingers and 2 left-hand fingers in an industrial accident without affecting his performance. A Celtic banjo player has a brace to relieve his carpal tunnel syndrome. A Celtic banjo has only 4 strings. A Bluegrass banjo has five strings and needs 24 frets. An Old Time banjo needs no more than 5 frets, and some don't need any. A Celtic banjo player flat picks everything. A Bluegrass banjo player puts jewelry on his fingertips to play. An Old Time banjo player puts super glue on his fingernails to strengthen them. Never shake hands with an Old Time banjo player while he's fussing with his nails.
Celtic and Bluegrass fiddles are tuned GDAE. An Old Time fiddle can be in a hundred different tunings. Old Time fiddlers seldom use more than two fingers of their left hand, and uses tunings that maximize the number of open strings played. Celtic and Bluegrass fiddlers study 7th position fingering patterns with Isaac Stern, and take pride in never playing an open string. An Old Time fiddle player can make dogs howl & incapacitate people suffering from sciatic nerve damage. An Old Time fiddle player only uses a quarter of his bow. The rest is just wasted. The Bluegrass fiddler paid $10,000 for his fiddle at the Violin Shop in Nashville. The Celtic fiddler inherited his fiddle from his mothers 2nd cousin in County Clare. The Old Time fiddler got his for $15 at a yard sale.
An Old Time guitarist knows the major chords in G and C, and owns a capo for A and D. A Bluegrass guitarist can play in E-flat without a capo. The fanciest chord an Old Time guitarist needs is an A to insert between the G and the D7 chord. A Bluegrass or Celtic guitarist needs to know C#aug+7-4. A Celtic guitarist keeps his picks in his pocket. Old Time guitarists stash extra picks under a rubber band around the top of the peg head. Bluegrass guitarists would never cover any part of the peg head that might obscure the gilded label of their $3,000 guitar.
It's possible to have an Old Time or Celtic band without a mandolin. Mandolin players spend half their time tuning their mandolin and the other half of their time playing their mandolin out of tune. Old Time and Celtic mandolin players use 'A' model instruments (pear shaped) by obscure makers. Bluegrass mandolin players use 'F' model Gibsons that cost $100 per decibel.
A Celtic band never has a bass, while a Bluegrass band always has a bass. An old, Old Time band doesn't have a bass, but new time Old Time bands seem to need one for reasons that are unclear. A Bluegrass bass starts playing with the band on the first note. An Old Time bass, if present, starts sometime after the rest of the band has run through the tune once depending on the players blood alcohol content. A Bluegrass bass is polished and shiny. An Old Time bass is often used as yard furniture.
It is not possible to have a Celtic band without a tin whistle or Bodhran (hand drum) if not several too many of each. Old Time and Bluegrass bands never have either. A Bluegrass band might have a Dobro. An Old Time band might have anything that makes noise including: a tambourine, jaw harp, didgeridoo, harmonica, conga, wash tub bass, miscellaneous rattles & shakers, a 1 gallon jug (empty), or a lap (mountain) dulcimer or a hammered dulcimer. In a Celtic band, it's the musicians that are hammered.
Except for the guitar, all the instruments in a Celtic band play the melody all the time. In an Old Time band, anyone can play either melody or accompaniment at any time. In Bluegrass bands one instrument at a time solos, and every else plays accompaniment. Bluegrass bands have carefully mapped-out choreography due to the need to for solo breaks. If Old Time and Celtic band members move around, they tend to run into each other. Because of this problem, Old Time and Celtic often sit down when performing, while a Bluegrass band always stands. Because they're sitting, Old Time and Celtic bands have the stamina to play for a square or contra dance. The audience claps after each Bluegrass solo break. If anyone talks or claps near an Old Time or Celtic band, it confuses them, even after the tune is over.
Personalities Stage Presence
Bluegrass band members wear uniforms, such as blue polyester suits with gray Stetson hats. Old Time bands wear jeans, sandals, work shirts and caps from seed companies. Celtic bands wear tour tee-shirts with plaid touring caps. All this headwear covers bald spots. Chicks in Bluegrass bands have big hair and Kevlar undergarments. Chicks in Old Time bands jiggle nicely under their overalls. There are no Chicks in Celtic bands, only Lassies with long skirts and lacey, high collars and Wenches in apple-dumplings-on-a-shelf bodices and leather mini-skirts. A Bluegrass band tells terrible jokes while tuning. An Old Time band tells terrible jokes without bothering to tune. Bluegrass band members never smile. Old Time band members will smile if you give them a drink. A Celtic band is too busy drinking to smile, tune or tell jokes. Celtic musicians eat fish and chips, Bluegrass musicians eat barbecue ribs, and Old Time musicians eat tofu. Bluegrass musicians have mild high frequency hearing loss from standing near the banjo player. Old Time musicians have moderate high frequency hearing loss from sitting near the fiddler. Celtic musicians have advanced hearing loss from playing in small pubs with all those fiddles, banjos, tin whistles and bodhrans.
A Celtic band travels in an actual Greyhound bus with marginal air conditioning and then catches a ride from the bus stop to the festival anyway they can. A Bluegrass band travels in an old converted Greyhound bus that idles in the parking lot all weekend with the air conditioner running full blast, fumigating the county with diesel exhaust. The Celtic Band has their name on their instrument cases and a banner for their Easy-Up. The bluegrass band's name and Inspirational Statement are painted on both the side and front of the bus in script lettering. An Old Time band travels in a rusted-out 1965 VW microbus that blows an engine in North Nowhere, Nebraska. They don't have an Easy-Up, and it's pretty evident that their vehicles don't have air conditioning. Bluegrass bumper stickers are in red, white and blue and have stars and/or stripes on them. Celtic bumper stickers display banners and slogans from the old country. Old Time bumper stickers don't make any sense (e.g. 'Gid is My Co-Pilot?) Bluegrass players stay on the bus and Celtic musicians at the nearest Motel 6 while Old Time musicians camp in the parking lot.