a shower thought occurred to me and as a non-formally trained musician I wonder if someone could quell my queries regarding this.
Say I have an interval, a G note followed by a C note, where the C is higher than the G. We can all unanimously agree that the interval is a perfect fourth. However, if we take reference to the C note instead, G would be the perfect fifth instead and we would call it a perfect fifth?
My confusion comes from the fact that the G is actually lower than C in this case.
Do we always take reference to the lowest note (G in this case) when pinpointing an interval, or are there any sort of rule in terms of which note to reference such that we could call the specific example a perfect fifth instead?