[Grammar] Spelling and grammar do matter

[Zunfix]

My teacher put this on the board a few weeks back.

Spelling and grammar do matter!

I thought it may be a ironic joke and asked her about it, she defended it telling me it's grammatically correct. I thought it should have read:

Spelling and grammar does matter!

Which is correct, if either?

 

[probus]

"Spelling and grammar do matter!" is correct. You have two subject nouns, so you use the plural verb.

 

[Raymott]

Sometimes, two subjects, if they are closely related can take a singular verb. This is what might be confusing you. (I'm sure your teacher explained this in her defence, but for those who weren't there, I'll give some examples.) The context is important.
1. "Language and Literature is my favourite class." You use the singular here because there is only one class called "Language and Literature".
2. Here is a list: vocabulary, morphology, phonetics and phonology, syntax, semantics. You can legitimately ask "Is phonetics and phonology on the list?" (Not "Are ..." because it counts as one item in the context.)
3. "This bacon and eggs is delicious!" You're talking about the dish, not the individual items.
4. "Spelling and grammar does matter!" could be OK in the right context. If in doubt, follow the normal rules and use 'do'.