Eric, this might be directed especially at you! :-)
On an example of a type of song/tune contruction found in folksongs of early origin:
"The form may be briefly outlined as follows. If letter A be taken to represent the 1st complete phrase of 4 measures, and B a secondary phrase, differing in melodic or rhythmic character from the 1st, then the formula AABA may be accepted as a representative type, and this will be found to be the general scheme on which the simplest songs are usually built."
- Granville Bantock
"The form may be briefly outlined as follows. If letter A be taken to represent the 1st complete phrase of 4 measures, and B a secondary phrase, differing in melodic or rhythmic character from the 1st, then the formula AABA may be accepted as a representative type, and this will be found to be the general scheme on which the simplest songs are usually built."
- Granville Bantock