Questions & Answers about O erro não é meu, mas a culpa é dele.
How does the word mas connect the two parts of this sentence?
The word mas translates to "but". It simply links the two contrasting halves of the sentence together. You do not need to change the word order or the verb forms in either half when you use it.
Why is "mine" translated as meu but "his" is translated as dele?
The word meu is a possessive word that matches the masculine noun erro. For "his", you might expect a similar word like seu. However, in Portugal, seu is often used for "yours" (when speaking formally). To avoid confusion, Portuguese speakers almost always say dele (which literally means "of him") to mean "his".
Why do we use é here instead of está for the word "is"?
Could I just say culpa instead of a culpa?
No, in Portuguese you almost always need the definite article (like o or a) before a noun. The word culpa is feminine, so it takes a. Even in sentences where English drops the word "the", Portuguese usually keeps it before nouns like erro (mistake) and culpa (fault).