Common Time

In music, Common Time refers to the 4/4 time signature. It means that each bar (measure) of music has four beats and that a beat is equal to a quarter note. It's so common that the notes (in American English at least) are pretty much named for it. Why else would a 'whole note' be four beats and everything else taken as fractions?

For some reason, 4/4 time is used in the overwhelming majority of rock and pop songs, to the point that it gives an impression of no other time signatures existing. A well-known joke among jazz bands is about a newbie trying (and failing) to read a piece written in 7/8 time, counting the beats "one - two - three - four - five - six - se - ven," being all too accustomed to 4/4 time. Classical music is rather more diverse in meter, with 2/2 ('Cut time'), 3/8, 6/8, and 3/4 being quite common.

Listing examples here is rather pointless. Rather, list the exceptions. It's just as pointless to list 6/8, 2/2 or 3/4, which are less common but just as unremarkable.

For more remarkable exceptions, see Uncommon Time.

Exceptions

 * Many of J-rock artist Miyuki Nakajima's songs are in 12/8 time: The beginning of "Massugu na Sen," "Itsutsu no Koro," and "Wasurerareru Mono Naraba", "Yasuko no Kutsu", "Doko ni Ite mo", "Hitori", "Revival", "Konban'wa" (12/8), "Tsuyoi Kaze wa Itsumo". "Akai Kawa" from Tsuki-wings is one of the more unusual examples, in 5/4.
 * The musical A Little Night Music is a full-scale aversion. Stephen Sondheim wrote most of the songs in 3/4, 6/8 or 3/2; "Send In The Clowns" is mostly in 12/8. The Cut Song "Two Fairy Tales" is the only song in Common Time.
 * Led Zeppelin were one of the earliest rock bands to deviate from common time, laying down the groundwork for metal bands for years to come. Sometimes, they were very subtle about it: most people miss the extra beat they add in to the pre-guitar-solo section of "Stairway to Heaven." Other times they were very blatant, such as in their song "The Ocean" which constantly switches between 7/8 and common. Notably, "Black Dog" was written by bassist John Paul Jones to have lots of time signature changes, but drummer John Bonham ignored this and played the whole song in Common Time. It shows.
 * Which actually makes the song harder to play as one really doesn't follow the rhythm. Yet it works!
 * Very, very many hymns are in 3/2 or 9/8. Many older ones are either in combined signatures (such as 6/4 + 4/4 combos) or in no set time signature at all. "Blessed Assurance," for instance, is in 9/8, and "O For a Thousand Tongues to Sing" is in 3/2.
 * 9/8 time has a numerological/religious significance for hymns. Three is considered a holy number, as it represents the Trinity, and thus three times three (=9) represents divine perfection. Three times three is often woven into other aspects of the structure of hymns and plainchants as well.
 * O Fortuna begins in 6/2 time, but is mainly in 3/2.
 * Richard Wagner's "Ride of the Valkyries" is in 9/8.
 * Unusually for an opera, Lohengrin comes close to being entirely in Common Time, the exception being the chorale preceding the duel. (The famous Bridal Chorus is in 2/4, but that's too similar.)
 * Except for the 4/4 bridge, "Electric Feel" by MGMT was in 6/4. Luckily for all those happy remixing people, it can be shoehorned into 4/4.
 * Gorillaz played around with this in at least one song, with drums in 4/4 and everything else in 5/4, occasionally switching to 4/4.
 * Martina McBride's "A Broken Wing" is in 12/8, which is basically 4/4 in jazz triplets.
 * Joanna Newsom uses this often. "Only Skin"'s main melody is in 12/8, but there are sections in 9/8, 3/4, and yes, Common Time. And that's not counting the isolated bars of 6/4. (The song's seventeen minutes long.)
 * Dave Brubeck's jazz albums Time Out, Time Further Out and Countdown were based on averting this trope, with various types of Uncommon Time used.
 * While the chorus of The Beatles' "All You Need is Love" is in Common Time, the verses are all in 7/8.
 * Happy and I'm / Smiling, Walking / Miles to drink your / water...
 * Living in the Past (5/4 time) isn't the only example of Jethro Tull using odd time signatures, but it's the most easily recognized. Other examples are:
 * The second 'movement' of Thick as a Brick - 5/8 time ("See there! A man is born...")
 * Most of the music from the entire Mega Man series is in 4/4 time, or an equivalent such as 2/2 or 8/8 (which is almost audibly indistinguishable anyway). However, a select few tracks are in other time signatures, such as Crystal Snail's theme from Mega Man X 2 (a combination of 6, 7, and 8 to a bar, changing at different points) and Blizzard Buffalo from X3 (3 beats to a bar).
 * As with Jethro Tull, a lot of prog rock (in many cases drawing on Brubeck or on classical music) is in Uncommon Time. For instance, the Supper's Ready segment "Apocalypse in 9/8" is precisely what its name says.
 * And unlike standard 9/8, which is divided into 3 groups of 3, "Apocalypse in 9/8" is divided as 4+3+2/8
 * In the Royal Conservatory of Music's grade eight repertoire, there is a song titled "O Moon", which completely lacks any time signature for a large portion of the piece.
 * Old British Broadsides are usually written down in mixed time signatures, reflecting the singer's personal style. This led to Percy Grainger recoring pieces in fractional time signatures - i.e. two-and-a-half quavers (quarters) to the measure.
 * Try playing "guess the time signature" with Dream Theater music. By the time you think you found it, it changes again.
 * Calgary indie rock band Women are rather fond of odd time signatures. They have songs in 13/8 and 7/4, and "Shaking Hand" has an opening riff that cycles through one bar in 13/8 and two bars of 4/4, and a closing section that cycles through one bar each of 3/4, 5/8, 3/4, 3/4, and 3/8.
 * The beginning of the Mission Impossible theme is 5/4.
 * So is "Everything's Alright" from Jesus Christ Superstar.
 * Movies often use variants on 3/4 for "epic" tunes. Think of the Pirates of the Caribbean and Harry Potter themes.