The phrase "a conviction that a" is correct and usable in written English.
It can be used when expressing a strong belief or opinion about something that follows in the sentence.
Example: "She held a conviction that a change in policy was necessary for the organization's success."
Alternatives: "a belief that a" or "an assurance that a".
The subtext of all this condemnation is a conviction that a Trump could never happen here.
It was a conviction. . . that a separation from the North was the only thing that could prevent the abolition of her slavery.. . .
What these two sharply different one-state visions share is a conviction that a two-state solution is out of reach.
In her memoirs, she wrote of him as a man possessing a "positive aversion to principle, even a conviction that a man of principle was doomed to be a figure of fun".
After a while, you have to ask whether it reflects a conviction that a thriving Jewish presence in the middle of the Islamic world is simply not acceptable to them.
I voted for Boris last time, partly because I hoped that he would take on the Tube drivers' union, but the decisive factor was a conviction that a third term for Ken would be a licence for cronyism.
But underlying Napier's sympathy for their plight is an apparent conviction that illness is invariably an opportunity for personal growth, a conviction that is hard to share.
Guesses included a sense of pride and a conviction that much work remained ahead.
"The petitioner should not be made to continue to serve a sentence for a conviction that has been vacated by this court, as it has been found unconstitutional".
"His incarceration was against the law, because it followed a conviction that could not be examined by a higher court".
"Ms. Kidman embodies this unstable amalgam with a conviction that is in itself terrifying," A. O. Scott wrote in The Times.
