Learn Polish: Mój brat nie powinien był tego zignorować. - My brother shouldn't have ignored it.

We use the negated modal word nie powinien (which matches the masculine subject brat) followed by the past tense particle był. Together, powinien był expresses that he had an obligation in the past, but the nie shows he did something he shouldn't have.

Why is the word tego in the genitive case here instead of the accusative to?

This is a classic example of the Genitive of Negation. The verb zignorować normally takes a direct object in the accusative case. However, because the modal verb powinien is negated with nie, the direct object of the attached infinitive must switch to the genitive case, making it tego.

Why is nie placed before powinien instead of before zignorować?

To express that someone shouldn't have done something, you negate the modal verb (nie powinien). If you placed nie right before the infinitive (powinien był tego nie zignorować), it would awkwardly mean that his duty was to actively not ignore it, rather than him simply making a mistake by ignoring it.

Why do we use the perfective verb zignorować rather than the imperfective ignorować?