saber de seguro

(v.) = know for + certain, know for + sure, know for + a fact

Ex. I know for certain I was moony and lonely, feeling dissatisfied with myself, and wanted only to be alone that night.

Ex. The whole extent of Chernobyl's damage -- both in terms of human casualties and environmental destruction -- may never be known for sure.

Ex. Here's the question: If you knew for a fact that you only had seven years to live, what would you do?.

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(v.) = know for + certain, know for + sure, know for + a fact

Ex: I know for certain I was moony and lonely, feeling dissatisfied with myself, and wanted only to be alone that night.

Ex: The whole extent of Chernobyl's damage -- both in terms of human casualties and environmental destruction -- may never be known for sure.

Ex: Here's the question: If you knew for a fact that you only had seven years to live, what would you do?.