When PODER is combined with SER it takes on the meaning, maybe, might be, could be.
Pode ser. Maybe.
Quem pode ser? Who could it be?
Você pode ganhar tudo! You might win everything!
PODER is usually conjugated in the singular forms because it’s most common that you are saying it might be, he/she/ might be ETC.
But you can use poder in any conjugation. SER is always in the infinitive for this expression though.
Eles podem ser corretos. They might be right!
Ser is irregular in the Imperfect Indicative tense.
✻ The Imperfect tense is used when talking about continuous or ongoing action in the past. Something that used to happen or, would (always) happen.
eu ➜ Ela era uma criança tranquila. (She was a peaceful child.)
você, ele, ela ➜ Era uma vez. (Once upon a time.)
nós ➜ Nós éramos vizinhos. (We used to be neighbors.)
vocês, eles, elas ➜ Vocês eram estudiosos na escola. (You were studious in school.)
Ser is for somewhat permanent characteristics. Don’t take this too literally – nothing is truly permanent 😉
very permanent ➜ Meu nome é Raquel. ➜ My name is Raquel.
somewhat permanent ➜ Eu sou brasileiro. ➜ I'm Brazilian.)
not so permanent ➜ Ele é casado. ➜ He's married.
Estar is for temporary passing things.
Eu estou cansado. (I'm tired.)
Como você está? (How are you?)
Ser & Ficar can often be used interchangeably in cases like these:
When talking about something permanent – a post office, the park, your home you can use either ser or ficar to describe where exactly it is, is located.
Onde é? ➜ O hotel é aqui. ➜ The hotel is here.
Onde fica? ➜ O hotel fica aqui. (same)
é ➜ É muito difícil. ➜ It's very difficult.
fica ➜ Fica muito difícil (same)
Ser & ficar can be used interchangeably to talk about the location of something:
When talking about something permanent – a bank, the park, etc, you can use either ser or ficar to describe where it is.
O hotel é aqui. (The hotel's here.)
O hotel fica aqui. same
Ser & Ficar can often be used interchangeably in cases like these:
é ➜ É muito difícil. (It's very difficult.)
fica ➜ Fica muito difícil. (It's very difficult.)