Questions & Answers about Ele tinha mostrado muita teimosia ontem.
Why is tinha mostrado used here instead of the simple past (mostrou)?
Tinha mostrado is the past perfect (pluperfect) tense, meaning "had shown". It describes an action that happened before another past event. While the second event isn't stated here, the sentence implies he had already shown this stubbornness before something else occurred ontem (yesterday).
Could I use havia mostrado instead of tinha mostrado?
Yes, you can. In Portuguese, the auxiliary verb haver can replace ter in compound tenses. Havia mostrado means the exact same thing but sounds slightly more formal or literary in everyday speech.
Since our current lesson is about the subjunctive, why is this sentence in the indicative mood?