Learn Portuguese (Portugal): Tive um problema urgente, por isso desmarquei o compromisso. - I had an urgent problem, so I canceled the appointment.

Por isso translates literally to "for that," but it is used exactly like "so" or "therefore" in English to show the consequence of an action. It connects two complete thoughts: the cause (tive um problema urgente) and the result (desmarquei o compromisso).

Why is it um problema? Doesn't the -a at the end make it feminine?

Normally, words ending in -a are feminine, but problema is a classic exception! Many Portuguese words of Greek origin ending in -ema or -ama (like o problema, o programa, o sistema) are masculine, which is why we must use the masculine article um.

Why are both tive and desmarquei in the simple past (pretérito perfeito)?

While having a problem can sometimes be a background description using the ongoing past (imperfeito), here tive is used because getting the problem was a sudden, completed event. It acted as the immediate trigger for the next completed action: canceling (desmarquei) the appointment.

How does the word desmarquei mean "I canceled"?