RE: [Harp-L] Why use the term "perfect" to describe a perfect fourth or a perfect fifth?

[Richard Hunter <turtlehill@xxxxxxxxxxxxx>]

John Neff wrote:
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<This is the most basic definition:
etc.

--which is good information, but doesn't answer the question posed in the title, which is not "what is a perfect 5th?" but "why is it called perfect?"

My wife once asked me why a "mole"--in scientific terms, a certain quantity of molecules--is called a mole.  The answer is: a mole is a certain quantity of molecules by definition.   

So the answer to this question is: a perfect 5th is 7 half-steps, by definition.  A perfect 4th is 5 half-steps, by definition. 

As to why the term "perfect" was chosen instead of something else, I suppose it might be possible to find the first use of the term in some medieval text, maybe even along with an explanation (which given the liturgical nature of early music would probably have something to do with these intervals sounding heavenly, especially in the temperaments commonly used at the time)--but that's a job for musicologists, not musicians.  

Thanks, Richard Hunter 



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