Like a good fugue the recent parliamentary debate on regional pay in the NHS had more than one major subject.
Its principal theme was stated by Labour: the move towards regional pay deals by a consortium of NHS trusts in the South West was a thoroughly bad thing.
The project exuded "unfairness, irrationality and economic illiteracy", we were told in the warm alto tones of Alison Seabeck (Lab, Plymouth Moor View).
From the government benches came an answering phrase in the rich bourdon of Geoffrey Cox (Con, Torridge and West Devon), who enthusiastically set about embroidering the same theme with his customary eloquence.
It was both "wrong and retrograde", he said, exhibiting a little of that talent for alliteration so admired by Professor Higgins in Alfred Doolittle. And it was "inconceivable" that he could agree to a policy which would further depress incomes in his already low-wage constituency.
Then he deftly introduced the counter subject: it was indeed a dastardly business but it was all Labour's fault.
Who is to blame?
He and his coalition colleagues from the South West went on to perform every conceivable variation on this motif. They were as appalled by the prospect of regional pay as the members opposite but Labour needed to do the decent thing and fess up to the fact that their own reforms had given trusts the power to pursue this option. It was, opined Geoffrey Cox, "cynically opportunistic" of Labour to try to wash their hands of the matter.
Labour insisted this was nonsense. The changes they had introduced had allowed one trust to increase pay in one instance but there had been no pay cuts on their watch.
As much of the ensuing debate seemed to be devoted to who was to blame as to the basic issue itself.
Andrew George (Lib Dem, St Ives) attempted a synthesis of the two themes: regional pay was bad and Labour had let it happen - but perhaps they hadn't really meant to.
Labour were still having none of it, so - unlike a good fugue - the subject and counter subject were not resolved in glorious harmony.
This is the House of Commons, though, so it was a minor miracle that the counterpoint proceeded as well and for as long as it did.
But it left the obvious question - how did we reach a situation where NHS trusts can negotiate regional or local pay deals - entirely unanswered.
My quest to get an answer started with the Foundation Trust Network.
They told me it was "complicated", something I'd already got half an inkling of. In broad terms, though, they said trusts had received the theoretical power to vary terms and conditions as long ago as 1990 under the Conservatives. But they claimed it was only after further changes made by Labour that this became a practical proposition.
Next I approached the consortium of South West trusts who are actually trying to implement these freedoms.
The consortium says it is basing its case firmly on the NHS 2006. So the trusts, which are the driving force in this, clearly think they have Labour to thank.
Finally, I sought a ruling from the Department of Health. Surely they could give me a definitive ruling on whether the move was legally sound and - if yes - which piece of legislation made it so.
The department says the powers are enshrined in the NHS and Community Care Act 1990 - a piece of legislation enacted by Margaret Thatcher's government.
They directed me to Schedule 2, paragraph 16, where it states: "An NHS trust may pay its staff such remuneration and allowances and employ them on such other terms and conditions as it sees fit".
The department threw no more light on the issue of whether Labour's later reforms had enhanced this. But the whole point of Labour's new foundation trusts was that that they should have more autonomy than their traditional counterparts.
The 1990 Act also stipulates that a trust's freedom to vary pay and conditions must be "in accordance with regulations and any directions given by the Secretary of State".
This would seem to support Ben Bradshaw's (Lab, Exeter) claim at the beginning of his debate on regional pay that "a single word from the minister today and this madness can be stopped".
It's not surprising that Health Minister Anna Soubry instead chose to commend the South West consortium for its "mature" and "responsible" approach.
A government which is seriously considering introducing local pay across the public sector can hardly be expected to censure others proceeding in the same direction.
The truly definitive ruling on all of this would probably involve testing it in the courts, which neither my personal means nor the BBC's licence fee allow for.
But Ben Bradshaw, at least, thinks others may well now do so.