Please note that these pages are about BRAZILIAN PORTUGUESE, not European Portuguese
PREPOSITIONS
de of, from em in, on a to (direction), at (time) por for (a favor for), out of, because of, from, by para for, to, towards
Indefinite article and preposition merge (contraction)
de = from Portugal, Portugal's
em = in Portugal, on the table
masculine feminine de singular dum * duma * em singular num numa * Colloquial use!!!! Avoid in written Portuguese.
Definite article and preposition merge
a = to Portugal, at three
de = from Portugal, Portugal's
em = In Portugal, on the table
por = for; out of, because of, from, by; through
masculine feminine a singular ao à plural aos às de singular do da plural dos das em singular no na plural nos nas por singular pelo pela plural pelos pelas
Simplified table (you can reason the blank places)
masculine feminine a singular ao à de singular do em singular no por singular pelo
(none at the time)!