I'm certain of your success. ✬

Please make certain your seat belt is fastened. ✬

We went early to make certain that we could get seats. ✬

I met a certain gentleman at the station. ✬

We were certain of winning the game. ✬

I don't know for certain. ✬

I didn't know for certain which train to take. ✬

No one knew for certain how the accident happened. ✬

Are you quite certain about it? ✬

The old cottage has a certain charm about it. ✬