Originally Posted by: Jolly McJollyson
A parellel third is when two voices move from harmonizing in thirds to harmonizing in thirds. As in, the bass is D and the soprano is F# then the bass is E and the soprano is G

Is it basically then harmonising based on the scale, i.e. both major and minor thirds are taken into account, so the interval between harmonies changes depending on the note being played - e.g for D Major, D E F# G A B C# where the harmony would be F# G A B C# D E)

If so, what would it be called if the interval betweens the notes stays the same, (e.g. always major thirds, again for D Major where the harmony would be F# G# A# B C# D# E) ?

I can't understand the difference between parellel thirds, and harmonising in thirds based on the scale - is it just the name given to it?