I recently joined in a conversation on a Facebook site called 'Learn Ukulele Free' when a great songbook was added by Jim Carey. There are hundreds of songs and he has produced a number of updates. This time (and probably previously) he asked for any problems to be mentioned to him so he could add errata. I wasn't going to get into detail because every song is open to interpretation, but I have noticed a common practice of naming dim7 chords dim. Here is the comment I made after Jim requested opinions...
for opening up the conversation Jim. I think music theory helps and I
hope this explanation helps too. Major chords take the 1st, 3rd and 5th
notes of the scale, e.g. C E G.
Minor chords take the 1st, flattened (or minor) 3rd and 5th notes of the scale, e.g. C Eb G
Diminished chords take the 1st, flattened 3rd and flattened 5th, e.g. C Eb Gb
7th chords take the 1st, flattened 3rd, flattened 5th, and add dim7th
e.g. C Eb Gb A. The differences between each of these intervals is three
semitones i.e the dim 7th of each of the notes within the chord always
has the other notes in it. You can start on any of the notes and you end
up playing the same four notes. So learn one and you are playing four
are 12 different notes, five of which have two different names. There
are only three different chord positions which are all the same shape,so
with one chord shape and three different positions you have 17
I was thinking about the importance of knowing the difference between dim and dim7 chords and whether it matters if the wrong label was on a chord chart as there were a few comments that it didn't matter.
I spent 26 years as a physio and the first year is spent learning anatomical names. Does it matter as long as I was treating the right bit? Well yes. It matters because it shows that I have learned a discipline and others can have confidence in my knowledge. It matters because I have communicated what I have done to others. It matters for many other reasons but I'll stick there and say it also applies to any other discipline, particularly when another muscle has a similar name but hasn't been injured.
All of these reasons apply to other areas of learning including music. However my main reason is that the dim and dim7 chords are different. The dim7 pattern is the one everyone knows and that's great, but what do you do if a composer just wants a dim chord? Nobody would know.