What was it that Nietzsche said? When you gaze long into David Cameron’s speeches, David Cameron’s speeches gaze also into you? That, at any rate, is what the past few days have felt like for me. Realising that next week’s conference speech could be Cameron’s last as party leader, I decided to revisit all of his previous ones. Almost a decade’s worth of conference jabber. Over 50,000 words. Gaze long, and soon phrases such as “let’s be clear” and “social responsibility” and “global race” start imprinting themselves on your everyday discourse. Your neural network is flooded with Camspeak. It’s no fun at all.

But it is educational. Conference speeches may just be so many words, but in combination they can tell the story of a leadership. That’s certainly what they do in Cameron’s case. What emerges from his speeches is a leadership in three acts. Sadly, the act we’re in now could probably be called “decline”.

The First Act begins with a conference speech that Cameron made before becoming party leader: his original pitch for the job in 2005. It wasn’t elaborate in any way. None of his speeches really are. What Cameron believes in, as I once explained in the Sunday Telegraph, is simple language that simply gets to the point. He’ll often take a marker pen to the work of his speechwriters, and edit everything back to its irreducible core. Much better, he thinks, for the TV news bulletins.

What made this first speech stand out, rather than its prose, was its audacity. The idea of modernising the Conservative Party was nothing new, but here was a relative newcomer preaching that creed without equivocation. It was optimistic: “I love my country. I love our character. I love our people.” But it was also firm: “Some say that we should move to the right. I say that will turn us into a fringe party, never able to challenge for government again.” Who the Hell was this guy?

Everything that might once have been called “Cameronism” was in that speech – even the Big Society, long before it became known as such. “We are the only party believing that if you give people freedom and responsibility,” he said, “they will grow stronger and society will grow stronger.” This idea of freedom tempered by responsibility may just be simple Burkean conservatism, but there’s no denying that Cameron was pushing it from the very beginning. That, and noble – if generic – nouns such as “aspiration”, “compassion” and “change”.

Cameron’s first speech as party leader, in 2006, was basically an extended version of his leadership pitch. It had that line about summing up his priorities in three letters (N, H and S, for those who weren’t listening at the back), but more important was its reliance on several other letters: R, E, S, P, O, N… oh, you get the idea. Cameron had returned to the subject of “responsibility,” or “social responsibility” as he more often called it. Again, this was the Big Society in prototype. As he described it, people had responsibilities to each other, and fulfilling them would strengthen all the ties that bind us together: “Our fundamental aim is to roll forward the frontiers of society.” This was the first time he’d say, “We are all in this together.”

The 2006 speech dwelt on some of early-Cam’s other favourite themes. There was a long section on the health service, of course. But he also spoke fervently in support of the family – “Families, to me, are not just the basic unit of society, they’re the best.” – and of marriage and civil partnership. And he took time to speak about climate change and to recommend that everyone “go and see Al Gore’s film, An Inconvenient Truth”. In fact, Cameron included a handy cut-out-and-keep list of the “things that matter most to me” at the end of the speech: “Family. Community. Society. The NHS. The environment. Our quality of life.”

These were the Lego bricks with which Cameron would build his next few conference speeches. He’d add more bits to the tower, but the same bricks would always come back. When you put them side by side, it’s almost boring how similar parts of the 2007 speech are to parts of the 2006 one. There’s the passage on strengthening society. The passage on the importance of the NHS. The passage on protecting the environment. The passage on family. If he said it last year, he said it this year. It’s as though he did actually care about this stuff.

The other thing these early speeches share is a freewheeling and confident tone. This is a leader who sounds sure of himself. “I don’t care,” is his blunt response, in 2007, to the notion that “it is not popular to talk about green issues.” He doesn’t mind disturbing the audience’s partialities by praising the Labour government. In 2006, it’s a straight-up admission that “not everything that Labour have done since 1997 is bad”. In 2007, it’s something even more gooily magnanimous: praise for Ed Balls.

When did all this change? Our Second Act begins in 2008. This was Cameron’s first conference speech since the great unravelling of the financial system – and boy does it show. The introduction to the speech is perfunctory. Only a few lines about how nice it is to be in Birmingham’s Symphony Hall, blah, blah. Then it’s straight into the rough: “Today the financial crisis means that all eyes are on the economy and the financial markets…” This was a more procedural speech than Cameron had delivered previously. Within the first minute he had already mentioned “our proposal to increase the protection for depositors to £50,000”. It was as though he had reached the “science bit” after years of flashing his glossy hair for the cameras.

The language was altogether darker. Cameron started relying on words such as “crisis” and “inefficient” and “anxiety”. But this was no bad thing in itself. Some of the boom-time certainties of his earlier speeches did need moderating. At last, he started attacking Gordon Brown for over-spending and over-borrowing. “The cupboard is bare.”

But, crucially, Cameron also stuck by much of what he had said previously. The Crash, for him, didn’t change the need for more supportive families or for a stronger society – it made them more important. It didn’t dampen his emphases on the NHS or on the environment – it made them more sonorous. The weather may have turned, but the Tory leader’s purpose didn’t appear to turn with it. He still professed his “faith in human nature in our remarkable capacity to innovate, to experiment, to overcome obstacles and to find a way through difficulties…”

This new rhetoric, of optimism despite it all, was at its best in 2009. This is my favourite of Cameron’s conference speeches. It contained everything, to a greater or lesser degree, that had come previously. But it also featured his most ferocious attack on the lazy presumptions of British politics. This is just an extract:

“Labour still have the arrogance to think that they are the ones who will fight poverty and deprivation.

On Monday, when we announced our plan to Get Britain Working you know what Labour called it? ‘Callous.’

Excuse me? Who made the poorest poorer? Who left youth unemployment higher? Who made inequality greater?

No, not the wicked Tories. You, Labour: you’re the ones that did this to our society.

So don’t you dare lecture us about poverty. You have failed and it falls to us, the modern Conservative Party to fight for the poorest who you have let down.”

The air thrummed with applause. A leader had properly found his cause.

Or had he? Well, no – because now the curtain opens on Act Three. Reading the four speeches that Cameron has delivered since, it’s as though he smashed down his Lego castle. Even the one from 2010, which is closest in proximity and tenor to those that had come before, is constructed differently. The NHS is barely mentioned. The environment is mentioned even less. The word “family” occurs only three times, or just twice in its old context. Some of the grand themes from Cameron’s previous speeches were suddenly less than leitmotifs.

Of course, it is different being in Government. Even more so than before, Cameron has to speak to the nation rather than to just his party. His rhetoric, just like his policy, has been constrained by being in Coalition with the Lib Dems. He cannot say that Labour are right when Labour’s entire purpose, as the party of Opposition, is to say that the Tories are wrong.

Yet, however many caveats you string together, it still feels like a surrender. It’s possible to keep on enumerating it – the word “environment” doesn’t crop up even once in 2011; “NHS” only got three throwaway appearances in last year’s speech – but the sense matters more than the numbers. And the sense is that Cameron’s attachment to these ideals is now, at best, sporadic. He has been diverted by new bricks marked “fairness” or “global race”. He changes them from year to year.

This isn’t to totally dismiss Cameron’s recent conference addresses. If anything, they are more delicate and considered than the ones he delivered before Government. For instance, his 2011 speech may have pruned back the greenery, but it also contained that eloquent case for gay marriage: “I don’t support gay marriage despite being a Conservative. I support gay marriage because I’m a Conservative.” His 2012 speech featured two moving tributes to his late father and to his son Ivan: “Today more people would see the boy and not the wheelchair.”

But the poetry is often let down by the politics. There hasn’t been anything to match the righteous anger of 2009 – unless you count the limp attempt to reheat it, last year, with the line “don’t you dare lecture anyone on the NHS again”. Instead, there was 2012’s speech and its “outrage” at “people getting 40, 50, 60 thousand pounds of housing benefit… We must be crazy.” The melody line, once so easy to follow, has become dissonant. Social responsibility has become the Big Society has become “facing up to this generation’s debts”. A-wha?!

You may disagree with my politics, and be left thinking: so what? Isn’t Cameron right about housing benefit claims? And who cares about all that green crap and BS? But this isn’t just a matter of agreement. It’s a matter of conviction. Look back at that list that Cameron once totted up: family, community, society, the NHS, the environment – “these are the things that matter most to me.” He used to talk about them all of the time; now he talks about them infrequently, if at all. Do they not matter to him now? Did they ever really matter to him? If the Prime Minister is not sure of his beliefs, few people will believe in him.

And if he doesn’t want to take it from me, how about from himself? It was Cameron who said, in his conference speech of 2006, that “real substance… it’s about character, judgment and consistency.” Draw a line under that last word. Italicise that last word. Type it in bold. Real substance is about consistency. If only that was still part of the Prime Minister’s personal lexicon.