The phrase "a decisive turn for" is correct and usable in written English.
It can be used to indicate a significant change or shift in a situation, often with positive implications.
Example: "The new policy represents a decisive turn for the company, leading to increased productivity and employee satisfaction."
Alternatives: "a pivotal change for" or "a significant shift for".
On the surface, the latest GDP figures hardly suggest a decisive turn for the better.
As Cam Cole writes in The Vancouver Sun, the Canucks were hoping the Luongo chronicles took a decisive turn for the good after his first-round near disaster against Chicago, but they were wrong.
And so as someone who would like to see the American economy return to growth, I am hopeful (though not particularly optimistic) that housing markets will soon take a decisive turn for the better.
It's hard to avoid the conclusion that Grès, like a number of artists whose bent was innately conservative, simply bet on the wrong horse at the start of her career, and when history took a decisive turn for the abstract, she stubbornly, obstinately, pig-headedly went the other way.
Our Housing Bubble Index has dropped into a freefall that rivals the dot-com bust of the late 1990s, and breadth has taken a decisive turn for the worse.
One cannot say, however, that it also represented a decisive turn from socialism to capitalism, for it was not clear to what extent the restructured planning system might embody other essential features of capitalism, such as private ownership of the means of production and the exclusion of political power from the normal operations of economic life.
And straight back with a very tasty encounter: Seattle and RSL resuming hostilities on Friday night with what could turn out to be a decisive turn in the kick for home in the Supporters Shield race.
On the second day of a ground offensive that could signal a decisive turn in the battle for Aleppo, Syria's largest city, rebels said they continued to fight in new neighborhoods and with new tactics, as the authorities bragged of heavy losses for foes of President Bashar al-Assad.
On the third day of a ground offensive that could signal a decisive turn in the battle for Aleppo, Syria's largest city, rebels said they were adopting their tactics to harass government forces, even though the authorities boasted of inflicting severe casualties on the rebels.
Are we seeing a decisive turn in UK politics?
A decisive turn came when a whistleblower contacted, among other people, a reporter at the Arizona Republic.
