Common Time

As we all learned from our music teachers, that funny 'C' symbol after the clef means "common time". Sssuuuurrre it does! Actually, the symbol 'C' is not the letter 'c' at all, but a half circle. In the 14th century the predecessors of our time signatures were invented. In the beginning there was only triple or perfect time, indicated by a circle, the perfect geometric shape. "Imperfect" or duple time, was indicated with a half circle. This indicated the number of beats, either three or two, in the measure. But they also had the ability to indicate whether these beats themselves divided into three or two subdivisions. This was indicated with a dot. A circle with a dot indicated three beats and each beat had three parts. In our metric notation we would show this as 9/8.  A half circle with a dot indicated two beats and each beat had three parts. We would show this as 6/8. But a simple half-circle with no dot indicated two beats, each of which divides into two parts. They called this tempus imperfectum cum prolatione imperfecta. "Common time" takes a lot less time to say, though. Here is an example from an old manuscript. You can see the time signature as a little 'c' on the second space from the top, right at the beginning after the clef--a C-clef on the bottom line:

From the Chansonnier Laborde