Por cierto

[poli]

I know it can be used to mean by the way, but can it also mean certainly?

[Rusty]

There are some who think it can be translated as 'certainly' in some contexts, 'certain' or 'true', in other contexts, but the majority of the time por cierto means 'by the way' (and similar wording).

[AngelicaDeAlquezar]

I agree with Rusty.

I'll just add that when there is no previous verb (except "ser"), or if it's separated by a comma, it's always "by the way" or similar expressions:

--Juan no ha venido. Por cierto, ¿no has hablado con él?
Juan hasn't come. By the way, have you talked to him?

--Se ha pedido que todos estén en sus casas. Nosotros, por cierto, no deberíamos estar aquí en la calle.
Everyone has been asked to remain at home. We, by the way, shouldn't be out here in the street.

--Tienes razón. No es, por cierto, a lo que me refería.
You're right. Anyway, it's not what I was talking about.


Also, I think that when it means "certainly", it's not exactly the expression "por cierto"; it's rather a "por" added because the previous verb needs the preposition:

--Tomamos por cierto lo que nos dijo, pero nos engañó.
We took what he said for true, but he lied to us.

--La gente da por cierto todo lo que se dice sobre la enfermedad.
People believe it's tru everything it's being said about the disease.

--Ten por cierto que siempre voy a estar contigo.
Be certain that I will always be there for you.

[poli]

Thank you Angelica for your very thorough explanation

[AngelicaDeAlquezar]

Glad to help!