thank you Alan its making more sense now, your explanations are testimony to a true understanding.

One more question pleased:
The notion of secondary dominants helps., and I take the point that a secondary dominant does not have to be seen in terms of the modal degree - .....I er... think....

So you have this modal dorian minor(say D) and you want its secondary dominant. I dont know how to find it except counting up to the fifth degree and then creating a triad on this note using the minor scale tones. This gives an A minor .. which is the Aeolian which you are stating it is not.

Obviously there is something I dont understand, perhaps you are talking harmonic or melodic minor?

I do notice that often in a minor key the fifth chord is 'substituted' with a 7th chord in order to give a cripsness and definition to the tension of this position perhaps it is simply this that is intended?

Is it simply that the secondary dominant is always a 7 chord and never anything else?

thanks for the input

Win 11 64, Asus Rog Strix z390 mobo, 64 gig RAM, 8700k