Please help me because I'm very stupid and my brain hurts.
I've been trying to make sense of the explanation of what constitutes consecutive fifths and octaves, and why/how to avoid them in both Harmony in Practise and my ancient copy of the little red theory book. Both the explanations are basically the same, but I am having trouble recognising them.
I understand that it is the interval of a fifth or an octave in a chord, and that you should not have 2 (or more) in a row - but how can this be avoided given that in 4-part harmony you must double something from a triad, thereby creating an octave on every chord? Is it simply that 5ths/8ves between the same 2 parts must not be consecutive? So you can have a 5th between Alto and Soprano parts, followed by one between Tenor and Bass parts - but not another consecutive A/S 5th? And also, does it still count as a fifth or octave even when separated by another octave/s (eg, low C to high G)?
As you can see, I'm not grasping this very well. Sorry if the above makes no sense at all, it's a symptom of my state of mind! Hopefully some kind person can untangle me.