"Si es, es" is Spanish for "If it is, it is". If you just mean "si es", that means "if it is". If you mean "Sí es" (with an accent on "Sí"), it means "Yes, it is".
"Si hoy es jueves, mañana es..." means "If today is Thursday, tomorrow is..."
"if it's not with you"
si es porque means if it's because
Si algo es "clinically proven," es probado por científicos.
If the party is everything.
If the movie is very interesting..
if you have msn, mine is...
Na es diminutivo de "nada". Nothing
What a sweet life it really is.
It translates to "if today is Monday, tomorrow will be."
tu es si belle et si sexy / tu es si beau et si sexy
He/she is a monkey.