Little is certain about his life, including when and where he was born.

Sorry I could not be more certain about the cause.

For the moment, I'm not quite certain about my future course of action.

She was no longer quite so certain about the quality of her work.

He was less certain about his future in the Army.

Now if only I could be so certain about the rest of my life.

No one is certain about the time when he lived.

He was now less certain about that than they were.

I am now less certain about that, as are others.

I'd not be too certain about the rest of the lot if I were you.