Constar

[poli]

Can you use consto que[/I ]to mean [I]estoy seguro que?

[JPablo]

Not really.

You can say something like, (in the sense of "quedar registrado")

El día en que me caiga, en que me hunda, ese día no [***]consto[***] en ningún libro, en ninguna nómina y mis vecinas tendrán que llevarme a la caridad pública, con la poca caridad pública que hay en esta ciudad.

AÑO: 1990
AUTOR: Vázquez Montalbán, Manuel
TÍTULO: Galíndez
PAÍS: ESPAÑA
TEMA: 07.Novela
PUBLICACIÓN: Seix Barral (Barcelona), 1993

[pjt33]

Constar seems to me to be mainly used in the third person, a bit like gustar. I think I most commonly see it as no me consta que ..., which I would translate roughly as I'm not aware that ..., but I think is more precisely I haven't seen evidence that ...

[aleCcowaN]

Can you use consto que[/I ]to mean [I]estoy seguro que?

Either "me consta que..." or "doy fe que..." are what you're looking for.

"me consta que..." = I have evidence, clear enough, abundantly enough, regarding what follows...

"doy fe que..." = I have evidence and or experience of something being the truth of existing so I can sort of "certify" it as if I'm some kind of notary. I'm so sure of this that I certainly can and will repeat it under oath.

Along the lines of the way you were using in your question, there is the expression "dar constancia":

"Doy constancia de que Fulano de Tal se ha presentado ante mí en el día de la fecha a ..." meaning, "I'm certifying it" whether because I'm authorized to do such a thing or because I want to back up what is declared using my reputation and honour.

[poli]

Thanks both of you. You have made this clear.