Making a convincing plagal cadence, how?

Jul 15, 2019

I am nearing the end of composing the first movement of my suite. And I plan to end the movement using a plagal cadence. But I know that a plagal cadence can be hard to make sound convincing, I mean after all, it is a subdominant to tonic motion. And most of the time if anything, the subdominant moves to the dominant for your classic IV V I or a slightly embellished version of the same cadence such as IV V vii°7 I

I know that part of making a plagal cadence sound convincing is to slow it down. V I could easily be convincing at quarter note speed. Not so easy for IV I to be convincing at that speed. But as you slow it down, IV I becomes more convincing. Another thing that makes the plagal cadence more convincing is having the upper voice move between scale degrees 5 and 6, implying a second inversion subdominant chord. 

Second inversion is the least stable form for any major or minor triad. And scale degrees 6 and 4 naturally want to move downwards. This leads to a convincing tonic resolution from the subdominant. Repeating the chords in a pattern like this


as it is in the Messiah Chorus, makes the cadence even more convincing.

But do I need to do anything else to make the plagal cadence convincing? Would a leaping bass make it more convincing like it does for an authentic cadence?