Though most of these number systems fell out of use by 1910, many are still in use and the word yan continues to mean "one" in some northern English dialects. The practice may also have given rise to the notion of counting sheep to lull oneself to sleep, possibly because the numbers were also a source of children's rhymes (such as "eeny, meeny, miny, mo").
In order to keep accurate records (e.g. of birth and death) and prevent animals from straying, shepherds must perform frequent head-counts of their flocks. Dating back at least to the medieval period, and continuing to the present in some areas like Slaidburn, farms were granted fell rights, allowing them access to common grazing land. To prevent overgrazing, it was vitally necessary for each farm to keep accurate, updated head-counts.
Though fell rights are largely obsolete in modern agriculture except in upland areas, farms are often subsidized and taxed according to the quantity of their sheep. For this reason, accurate counts are still necessary, and must be performed frequently.
Generally, a count is the first action performed in the morning and the last action performed at night. A count is made after moving the sheep from one pasture to another, and after any operation involving the sheep, such as shearing, foot-trimming, mulesing, etc.
Sheep-counting systems ultimately derive from a Celtic language, possibly Welsh, Cumbric or the speech of a British population surviving after the Anglo-Saxon conquest. It is impossible, given the corrupted form in which they have survived, for us to be sure of their exact origin. One major tendency is that certain pairs of adjacent numbers now resemble each other by rhyme (notably 1 and 2, 3 and 4, 6 and 7, or 8 and 9), even though this probably was not the case in the original language. Still, multiples of five tend to be fairly conservative, such as 15, "bumfit" in most varieties, versus Welsh pymtheg.
Like most Celtic numbering systems, they tend to be vigesimal — based on the number twenty. Moreover, they usually lack words to describe quantities larger than twenty (though this is not a limitation of modernised decimal Celtic counting systems). To count a large number of sheep, a shepherd would repeatedly count to twenty, placing a mark on the ground, or move his hand to another mark on his crook, or drop a pebble into his pocket to represent each score (e.g. 100 sheep = 5 score sheep).
|20||Jiggit||Gun a gun||Jiggit||Jigget||Jiggit|
|Number||Derbyshire||Weardale||Tong||Kirkby Lonsdale||Wensleydale||Derbyshire Dales||Lincolnshire|
|15||Bumfitt||Tic-a-bub||Bumfit||Boon, buom, buum||Bumfitt||Bumfit|
|13||Tedder-a-Dick||Tethera - Dick||Teddera Dick|
|14||Medder-a-Dick||Methera - Dick||Meddera Dick|
|Number||Proto Celtic||Old Welsh||Welsh||Cornish (Kemmyn)||Breton|
|1||*Oino-||Un||Un||Unn (definite), Onan||Unan|
|2||*Dwā(w)-, *Dwei (f.)||Dou||Dau, Dwy (fem)||Dew, Diw f.||Daou|
|3||*Tri-, *Tisres||Tri||Tri,Tair (fem)||Tri, Teyr f.||Tri|
|4||*Kweteres, *Kwetesres||Petuar||Pedwar, Pedair (fem)||Peswar, Peder f.||Pevar|
|11||Un ar ddeg||Unnek||Unnek|
|13||Tair ar ddeg||Trydhek||Trizek|
|14||Pedair ar ddeg||Peswardhek||Pevarzek|
|16||Un ar bymtheg||Hwetek||C'hwezek|
|17||Dwy ar bymtheg||Seytek||Seitek|
|19||Pedair ar bymtheg||Nownsek||Naontek|
The English composer Harrison Birtwistle (b. 1934) composed a chamber opera entitled Yan Tan Tethera (subtitled "a mechanical pastoral") in 1984. It is about shepherds, and includes sheep being counted using 'Yan Tan Tethera' and the rival 'One Two Three' system.
English chansonnier Jake Thackray wrote, performed and recorded a song about a shepherdess, entitled Old Molly Metcalfe, with the refrain Yan Tean Tether Mether Pip she counted. In the introduction to the song he describes how Swaledale sheep farmers "count their sheep in a curious fashion," and gives the entire sequence from 1 to 20.
In The Mating of Lydia, Mrs Humphrey Ward) the following counting rhyme is quoted of being from the northern dales. "Yan--tyan--tethera--methera--pimp--sethera--lethera--hovera--dovera--dick--Yan-a-dick--tyan-a-dick--tethera-a-dick--methera-a-dick--bumfit--Yan-a-bumfit--tyan-a-bumfit--tethera-a-bumfit--methera-a-bumfit--giggot"
In Terry Pratchett's novel The Wee Free Men the heroine, Tiffany Aching, is called "little jiggit" by her Grandmother, a female shepherd, as Tiffany was her twentieth grandchild; also, the titular race of sheep-stealing fairies, use the "yan-tan-teth'ra" sequence for counting off.
Yan Tan Tethera is the name of a book by David Herter related to his first novel, Ceres Storm.
Joan Aiken's children's book The Cuckoo Tree features ten "Gentlemen" named Yan, Tan, Tethera, Methera, Pip, Sethera, Wineberry, Wagtail, Tarrydiddle and Den.
The children's album "Fiddle Up a Tune" by Eric Nagler features a song "Yan Tan Tethera," whose eponymous phrase begins an incantation used to calm leprechauns: "Yan tan tethera, one two three: All you little ones, let us be. Hevapin sethera, four five six: Lay down your magic fiddlesticks."
It is also worth noting the number theory behind the scheme. Although decimal up to 10, in most dialects the scheme then changes to counting in base 5. It is possible to carry out limited arithmetic in base 5 on numbers up to 30 (decimal) using your fingers as a rudimentary abacus. It is pure speculation, but there may be a connection between the two facts, and the shepherds of England may have carried out limited accounting on their fingers.
One reason for the use of base five is suggested by the design of the shepherds crook which has grooves, nobbles, nicks or other impressions on it to enable the shepherd to note the number of fives counted on the other hand. He might also have had a handful of pebbles, putting one in his pocket each time he reached 20. Using base five counting in this way allows the shepherd to total as many sheep as the markings on the crook will allow, each mark representing five sheep.