Where Tony Abbott was defined by what he promised to stop, oppose or end, Turnbull is defining himself by what he hopes to achieve.

He not only wants to change a raft of policies, he wants to change the way Australia makes policies. He wants to change the way the country works. "I am a reformer by nature, very much so," he tells Fairfax Media.

Most profoundly, he wants to change the culture; the culture of government, the culture of politics, the culture of business. Even the way Australia presents itself to the world.

He cites the founder of modern China, Mao Zedong, in a famous declaration attributed to him in the creation of the People's Republic of China in 1949 when he said: "The Chinese people have stood up!" And Turnbull adapts it for Australia: "Modern China is built upon an assertion of national sovereignty. And that is why we say to China, 'The Australian people stand up!"' repeating it in Mandarin.

"So we stand up for our interests and our sovereignty," Turnbull continues, "and we engage with China and indeed with any other country, clear-eyed, honestly explaining what is in our national interest." 

'Tony Abbott and I are different people'

As a newly minted prime minister, Turnbull has made millions of his admirers fret.

The champion of same-sex marriage, climate action and a republic has explicitly committed to all the policies of the Abbott government, a regime that was suspicious of such progressive politics.

"Is Malcolm Turnbull sacrificing his principles?" asks John Menadue, a distinguished former diplomat, businessman and aide to Gough Whitlam. He wants to know what's happened to Turnbull's progressive vision. "Is it still there?" he worries.

While the Prime Minister handles the direct question with the delicacy of a glassblower – "Tony Abbott and I are different people" – it's clear from his broader comments that his ambitions are just about boundless.

One hint hangs on the wall as you walk into the Prime Minister's office. Tony Abbott's official portrait of the Queen is no more, replaced by an Australian landscape from Turnbull's private art collection. It's a wink, "fear not, it's still me".

But to change anything beyond the artwork, the precondition for Turnbull to succeed in any reform is to hold power long enough to accomplish it. 

And that means he needs to do what Kevin Rudd, Julia Gillard and Tony Abbott could not, what Joe Hockey urged this week: "The revolving door in Australian politics must be jammed shut," the former treasurer said in his valedictory speech to the Parliament. "If we don't show enough respect to each other then how can we hope that the electorate will respect us? ... We cannot make it normal to have four prime ministers and four treasurers in just four years." 

Hidden grudges and unabated anger

This is Turnbull's bedrock priority, yet the manner of his ascendancy is a poor way to prepare the ground. He took the prime ministership under the cloak of secrecy and in the name of opinion-poll popularity. 

The political execution of Abbott has left hidden grudges and unabated anger in the Liberal Party's ranks. And, declaring his challenge to Abbott for the leadership, Turnbull said: "We have lost 30 Newspolls in a row. It is clear that the people have made up their mind about Mr Abbott's leadership." 

This was true, but was it wise to say it with the whole country as witness? With those words, Turnbull armed any future challenger with a readymade justification. If there comes a phase where his government is behind in the polls for a year and a half, Turnbull will have to accept the right of any rival to challenge him. 

He has explicitly tied his fate to the polls. In short, he has set up the preconditions for yet more leadership instability, not less.

To establish solid ground for a long run in power, Turnbull needs to tend to his party's unity and good management ahead of his reform impulses. 

He has to do the very opposite of Menadue's former employer. On winning the 1972 election, Gough Whitlam and his deputy, Lance Barnard took upon themselves all 27 ministerial portfolios and operated a two-man government for two weeks. 

They barnstormed through some 40 decisions in 14 days. The "duumvirate" ordered all Australian forces out of Vietnam, the independence of Papua New Guinea, diplomatic recognition of China, an end to the ban on advertising contraceptives, an end to Australian knights and dames, a judicial inquiry into Aboriginal land rights, the decentralisation of universities and much more. That done, Whitlam appointed a full ministry. 

Banishing the scare campaign

John Menadue this week wrote that "a strong leader imposes his views on the organisation he leads and not the other way around". But Whitlam had fundamentally reformed his party and won an election. Turnbull has no such mandate and no such strength. He won his party room ballot by 54 to 44 and has yet to face the people. 

Much as Turnbull would love to declare an Australian republic with the words "the Australian people have stood up", he is resisting all urges to imperiousness. He has pledged commitment to a traditional cabinet government and full consultation. 

This is the essential lesson of his first and failed term as Liberal leader. He was determined to lead towards a carbon emissions trading scheme while Tony Abbott led an insurrection against him. Wherever he goes, he has to take his party with him. 

Yet even within this overriding constraint, Turnbull is speaking explicitly about transformational change in the way Australia operates. One revolutionary idea is keeping policy options open and seeking to banish that staple of politics everywhere – the scare campaign.

When we asked him which tax concessions he was prepared to review – superannuation, negative gearing, capital gains – he replied: "Everything, every single element, is on the table. And I know that always means that someone can then run a scare campaign, but I'm sorry, we've got to stop [this].

"This is part of the political tradition I'm determined to end. We have got to be able to consider policy options in an unfettered way. We've got to have the maturity to have a debate that is not throwing things off the table ... 

"Because what happens is politicians who get intimidated by their opponents or by the media or whatever, they say, 'Oh that's off the table, that's off the table, that's off the table' and suddenly there's nothing left on the table.

"And that is exactly what happened with the Henry tax review" under the Rudd government. "All of that work done and they ended up with that really misconceived resources super profits tax," which, as amended by Julia Gillard, raised no serious revenue and eventually was repealed by Abbott.

Talking big

He's right, of course. But it is a Utopian vision of good government. It's easy to say in a five-week-old government, in the full flush of an electoral honeymoon, that faces a flat-footed opposition and with a year before the next election is due. 

But if Labor decides to run a scare campaign in the prelude to the election, and if it starts to bite, he will come under intense pressure to do precisely what he seeks to avoid – to rule out unpopular policy options.

There's a reason parties run scare campaigns – they work. Ask Paul Keating about his scare campaign against John Hewson's Fightback, John Howard about his against "L-plate Latham" or Tony Abbott's against Labor's "great big new" carbon tax.

In specific policy areas, too, Turnbull is talking big. So long as it's not an internally divisive subject like same-sex marriage, he considers that he has room to move. He wants to trigger a big surge in Australian spending on infrastructure by changing the way the federal government has always operated.

He cheerfully admits that this is "an argument I lost in the Howard government" as minister responsible for water. It's now urgent with the economy slowing as the mining boom recedes. Infrastructure investment will partly take up "the slack", he says: 

"It takes advantage of the fact that money has never been cheaper," with record low interest rates on the world markets. But we've got to make sure we're borrowing to invest in sound economic infrastructure." How to do that? 

"I think the Commonwealth should take a more active role," he tells Fairfax Media. "We should be prepared to actually invest as opposed to simply making grants.

"Why do we keep writing out these big cheques? This is big economic infrastructure. We should be taking a piece of it. We don't need the same internal rate of return as Macquarie Bank would, obviously. But if we have a piece of it, then we're able to invest more, frankly. Then we're much better off being a partner rather than simply being an ATM." 

Cautious and judicious revolution

State and local government and private businesses too can invest in projects. He says he has no particular target figure for investment, but says the scope is enormous. 

When there is any sign that the government is veering towards the internally divisive issues that Turnbull has long championed, the conservative element of the party will not stand mute. 

We saw a glimpse this week when a Liberal Party advocate of same-sex marriage showed signs of impatience. Eric Abetz, the former leader of the government in the Senate and now the new informal leader of the internal opposition, immediately issued a public warning against any "ambush" on the subject. 

Turnbull has revolution in his mind and his heart. But, unlike Mao's violent upheaval followed by unceasing internal repression, Turnbull can not risk any further destabilisation by ruling as a repressive dictator. His revolution must be a cautious and judicious one. Unless the door stops revolving, there can be no Turnbull revolution.

He warned however that while this week's interest rate rises by banks were a commercial matter "there's always the potential" for such rises to harm a soft economy, describing them as "a very big signal" and their impact on household budgets "a significant one".

"Let me put it this way, the justification that they gave was not sufficient to explain the level of the increase that they made, in our view," he said.

And in the same week he celebrated the passage of the China-Australia free trade agreement through the House of Representatives, he said it was nonetheless critical that Australia spoke frankly to Beijing against its strategic expansion in the South and East China seas.

"Modern China is built upon an assertion of national sovereignty, and that is why we say to China, the Australian people stand up ... we have to be very, very clear-eyed in what we are seeking to achieve," he said.

Stressing innovation and adaptability, the Prime Minister, who weeks ago embraced the creativity of the National Reform Summit, reiterated that all policy ideas were back "on the table" including, in sharp contrast to the Abbott-Hockey approach, those on the revenue side of the budget.

That switch has left open the prospect of new or increased taxes, and of clipping back tax breaks for the wealthy – as Labor has proposed for superannuation – to deal with a budget facing problems he acknowledged were on both the revenue and spending sides.

"Everything, every single element, is on the table, and I know that always means that someone can then run a scare campaign, but I'm sorry, we've got to stop … this is part of the political tradition I'm determined to end. We have got to be able to consider policy options in an unfettered way," he said.

One of those has already found favour: an enlarged role for the federal government under the Turnbull leadership. It could see important economy enhancing projects, including roads, urban public transit, ports and water infrastructure, financed directly through Commonwealth borrowings or in partnership with state and local governments and the private sector, taking advantage of historically low interest rates.

Arguing such thinking "changes the paradigm", he said it made more sense for the Commonwealth to "have a piece" of major infrastructure, than to simply dish out grants and walk away.

"We don't need the same internal rate of return as Macquarie Bank would, obviously, but if we have a piece of it, then we're able to invest more, frankly," he said.

"Then we're much better off being a partner rather than simply being an ATM, for which you get generally scant thanks or recognition."

Also dispatched to history from the Abbott-era was the edict that urban rail was the exclusive province of state governments.

"We shouldn't discriminate urban mass transit, urban rail. It's sort of a penetrating glimpse of the obvious. I know it's change but, why would you discriminate between one mode of transport and another?" he argued.

Asked about one of the key foundations of policy under former treasurer Joe Hockey, who had famously lectured Australians about their entitlement mentality, Mr Turnbull was equally clear. "I wouldn't use that language," he said.

Those comments were a flat repudiation of the parting words of Mr Hockey, who told Parliament on Wednesday that his 2012 "end of the age of entitlement speech" had been the most significant single contribution to the national economic debate in 20 years.

But in a sign of the sensitivity of his role at the helm of a still shocked and divided party room, Mr Turnbull was measured when asked what had changed materially since his promotion.

"Well I am who I am, with any change of leadership of a political party, especially one that's in government, there are many elements of continuity and also elements of change," he said, noting he had been in the job for five weeks.

"But people can already see changes, there are changes of direction, changes of style, Tony Abbott is Tony Abbott, and [he and] I are different people."

On other areas, he indicated that his government would deliver a 2016 budget, dismissing suggestions of an election before the three-year term is up in September.

Also brushed off was the prospect of a political stoush with Labor over penalty rates, which he said was a matter for the Fair Work Commission.

- Peter Hartcher, Mark Kenny