It has come to my attention that the interval section in the Grade 4 ABRSM theory book may require a little more explanation for some theory learners. Below is a pdf of how I suggest to work out an interval in Grade 4.
Recently I found a copy of the “Text-Book of the Rudiments and Theory of Music” Grade 3 (Junior) for the Trinity College of Music published in 1937. There is a detailed explanation for how to work out an interval at this level.
It states that one must work out the numerical value of the interval first. And, it discusses using scales/keys to work out the higher note of the interval by using the lower note as the tonic of a key.
Following this they suggest that if the lower note is not a possible keynote or tonic, then it should be raised or lowered a semitone so that it becomes manageable. However, of course the names of the notes must remain the same.
Another piece of advice they give is a reminder to remember the key signature and how that affects any of the notes present in the interval.
It states ‘Never attempt to use the minor scale to find or measure intervals. The major scale is the only standard of measurement’.
Also it states that always work upwards from the lower note even though this note may be written after the upper note.