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He wants to mix it up in terms of ages and years of political experience, and Mr Bridges and Ms Kaye represent the party's new generation.
The extent of the Prime Minister's reshuffle took many by surprise, not least the two ministers whose resignations he required, Phil Heatley and Kate Wilkinson.
They had done a good job and done nothing wrong, he said, but it was time to make room for other talent in the Cabinet.
"They have had four years to make a great contribution. They have been good ministers but I want to give other people a chance.
"For National it is very important that we have constant renewal, that there are fresh faces coming through."
It was also important for National's longevity, he said, to have that mix of people with experience and to provide opportunity for others.
"If I was to look back to Helen Clark's time as Prime Minister, I don't think she renewed her Cabinet terribly well very often, and only by necessity."
That left Labour in disarray for the past four years.
"I am very committed to making sure there is a strong breadth and depth of talent at various different stages of their development coming through Cabinet."
Kate Wilkinson and Mr Heatley had both been disappointed but had pledged to remain "team players" from the backbench and they understood his thinking.
Amy Adams and Mr Bridges, both tipped as potential leaders, are among those who have been promoted.
Two new ministers were named: National's senior whip, Michael Woodhouse, outside Cabinet, and Nikki Kaye straight into Cabinet.
Mr Woodhouse's whip's role is likely to be taken by Taupo MP and junior whip Louise Upston when the party caucus meets next Tuesday.
Hamilton West MP Tim Macindoe is tipped to become junior whip.
His and Ms Kaye's appointment will leave vacancies on two select committees, education and justice and electoral.
Nick Smith has been returned to the Cabinet. He resigned last March after the Herald revealed he had written a testimonial in 2010 supporting a friend's ACC claim - at the time he had been ACC Minister.
But he has not got back his old jobs, Environment and Local Government.
He has Conservation and Housing and Mr Key indicated Dr Smith would be assuming responsibility for housing affordability, an issue Finance Minister Bill English has been leading, not just state housing.
Mr Key said Dr Smith would be working with local governments on housing affordability issues.
"He's a guy with lots of energy and ideas and he doesn't leave too many stones unturned. I think we can see in the housing sector him thinking right across the spectrum and working with a lot of different ministers to get results."
David Carter is set to be elected Speaker next Thursday to replace Lockwood Smith, who is leaving to be High Commissioner to London.
Mr Key defended his decision to keep Education Minister Hekia Parata in place despite the major upheavals of last year, including class sizes and Christchurch school restructuring.
She had been in her job for only a year, he said.
She had made mistakes but she had got a lot of things right. "I am very confident she is going to make it. There are one or two minor issues but there is a huge amount of talent there.
"She has got a new chief executive [Peter Hughes], she has got a new associate minister [Nikki Kaye], one of the big issues would be handled by Steven Joyce, it's a new year."
Mr Joyce will take responsibility for the Novopay teacher-pay debacle, with Mr English.
"If I were the providers of that system," said Mr Key, "I'd be on notice."
- Audrey Young of the New Zealand Herald