tenho a certeza de que

i'm sure that

→ ter
phrase Rare #37,692
i'm sure that Literally means “I have the certainty that.” The negative form, não tenho a certeza de que, means “I'm not sure that.” It is often followed by the subjunctive when expressing doubt or uncertainty.
PO: Tenho a certeza de que ela vai gostar do presente.
EN: I'm sure she'll like the present.

Tenho a certeza de que ainda vou sofrer muito.

I'm sure I'm going to suffer a lot more.

Tenho a certeza de que não vinha ninguém com ele.

I'm sure no one was coming with him.

— A Grande Escapada (1966)

Eu não tenho a certeza de que Tomás esteja feliz.

I'm not sure that Tomás is happy.

Não tenho a certeza de que o Tom quer fazer isso.

I'm not sure Tom wants to do that.

Tenho a certeza de que o fizeste de propósito, tu és .

I'm sure you did it on purpose; you're mean.