"I do not consider him a good father."

Translation: Já ho za dobrého otce nepovažuju.

[BrandonCas821536]

What is the rule on use of "za," please? When should it be used and for what purpose?

[VladaFu]

For various purposes. Generally, za means "behind", sometimes "after" sometimes "for". Here it is connected with the verb: "považovat někoho za"="consider somebody (as) something" Different verbs require different prepositions and you have to learn them individually.

[skrocic_o_]

Is that grammatically correct to say: "Nepovažuju ho za dobrého otce."?

[BoneheadBass]

"Nepovažuju ho za dobrého otce" is accepted.

[Nathalie126709]

Could you please explain why "dobrého tatínka" is not accepted ?

[VladaFu]

We currently distinguish the formal otec (father) and the informal (taťka, tatínek...).

We do not claim that the border lies exactly at the same spot in both languages and there may be some changes in the future.