Qfyilyi

I'm wondering whether a comma should precede the pronoun 'you' in the sentence examples below:

1. That's not how the computer works, you fool.




2. Thanks for the assignment tips, you saviour.

Whenever I usually write, I always place a comma before the pronoun in sentences like the examples above. However, I haven't really found anything that corroborates the notion that this is 'correct practice'. It is just something I have seen and copied. It would be helpful if someone can correct or explain this to me.

Any responses are much appreciated.

P.S. As an extra piece of help, is the pronoun 'you' an object in the first sentence and a subject in the second sentence? Is it an object pronoun in both? Thanks in advance for any responses to this as well.

Some sort of delimiting punctuation is indeed required there. Usually it's a comma, but e.g. an em dash sometimes works as well.

Discussion

In your first sentence, the phrase you fool is a noun phrase (NP) , where fool is the head and you a determiner. In that sentence, this NP serves in a vocative function (CGEL
, p. 353, note 14) . (In many languages, the noun fool would have to be in the vocative case.) Instead of you fool, you could put there any other legitimate vocative: a personal name (e.g. John), a kinship term (mom), a status term (Your Majesty), an occupational term (officer), a 'general' term (buddy), a term of endearment (dear), a (stand-alone) derogatory term (idiot, without the you), or a compound determinative (everyone).

And it is indeed a rule of English that an NP in the vocative function must be set off from the rest of the sentence by delimiting punctuation (CGEL, p. 1745).

As far as your P. S. question: when something is set off by punctuation, this normally signals that the thing being set off is not integrated into the syntactical structure of the sentence, and so it could not possibly be a subject or an object. Only in imperatives can there be a question of whether something is the subject or a vocative (CGEL, pp. 927-928).