Proper nouns in English have a capital starting letter and the plural is simpler (e.g. -y ending gets -ys instead of -ies).
Are there any other differences? Especially when analysing/parsing the grammar?
So this question is about which grammatical consequences does it have to the rest of the sentence if I find a proper noun. For example, is there some grammar that works only with proper nouns? Or grammar that doesn't work with proper nouns?
The question is less about on how to distinguish them in general.