His doubt hardened into certainty when she asked, "Do you think that the young man was to blame for the tragedy?"

But in such a situation a single moment suffices to change the strongest doubt into certainty.

By evening Anita's imagination had turned her fears into certainty.

She had the horrible feeling, fast growing into certainty, thathe and no other was behind this attack.

An idea, at first vague and uncertain, was gradually being changed into certainty.

An examination of the body turned our suspicions into certainty.

The end, he came to realize, was rapidly crystallizing into dead certainty.

As they passed more security stations, her suspicion hardened into certainty.

This suspicion hardened into certainty in the days that followed.

Any set of ideas can harden into ideological certainty, especially when it's been in power for a long time.