grammaticality - Difference between "did + verb" and just "verb+ed"

"Did + verb" isn't actually it's own tense, like "has + verbed" or "had + verbed" both are. Instead, the difference is merely emphatic.

She sang in the school play.

There's no special tricks to understanding this sentence, it's exactly what it sounds like. In the school play, which was in the past, the person you're talking about sang. This just sounds like you're telling somebody a fact about another person (she), and the context of the rest of the discussion isn't really relevant.

She did sing in the school play.

The actual meaning of this sentence is still the same. She sang in the school play. However, you're now emphasizing the truth of the sentence. This is very bizarre wording if you're just stating a fact with no other context. It's likely that, if you chose to word it this way, you said something before hand, such as:

• She says she never sings in public, but back in high school she did sing in the school play.


• Her father doesn't remember, but she did sing in the school play.


• She didn't perform in the talent show, though she did sing in the school play.

The most obvious and common use will be in situations like this, where her singing in the school play provides a direct contrast to what was said immediately before, but that's far from the only time it's correct to be emphatic.

She has such a beautiful voice. After all, she did sing in the school play and the competition for the role was pretty fierce.

As a note, in all of the examples I've listed, you can just say "sang" instead of "did sing." It is not at all incorrect, it simply doesn't have the same emphasis that "did sing" does.