Interrupted/deceptive cadence

[Belle-vue]

Hi,
In strict 4 part harmony rules, I don't get why the 3rd must be doubled in the VI chord in an interrupted aka deceptive cadence. I don't get parallel 5ths or 8ves when I just double the tonic.
Thanks in advance.

[Farnaby]

Can you expand on the chords involved in the cadence (there must be more than one), e.g. V-I or IV-I for example.

[jancivil]

The guideline regards V - root position VI in minor.
So, eg., key is G minor, here’s D - doubled root in root position - to Eb.

I think doubling the third of VI is preferable aesthetically, in that it’s the tonic note. I don’t recall it being a hard rule that gets points taken off in the exam. But it’s been 44 yrs.

[Farnaby]

It is difficult without reading a score. Are you assuming the cadence is V-vi, for example (in C major) G maj to A min. Or (in G minor) D to E flat minor? I can't quite work out what you are saying here. I'm sure Bach would have a way around it somehow.

[jancivil]

The VI of G minor is Eb major.

The “rule”, again, regards root position VI in minor.

Here’s a clear solution:
(In G minor) D to Eb, D to Bb. F# to G, A to G. Much the same as V7 to VI, the C there to Bb.

[Farnaby]

The VI of G minor is Eb major.

The “rule”, again, regards root position VI in minor.

Here’s a clear solution:
(In G minor) D to Eb, D to Bb. F# to G, A to G. Much the same as V7 to VI, the C there to Bb.

Yes Eb major of course.
I follow you now - thanks.

[Belle-vue]

I think doubling the third of VI is preferable aesthetically, in that it’s the tonic note.

I'm going to go with this as a very reasonable reason to follow the rule! Without such a valid reason, it's hard to come to terms with following rules!
Thank you