Learn English – “He is demanding that the father ‘pay’/’pays’ him $600”

In a previous question it has been asked (or should it be "it was asked"?) whether "He is demanding my father to pay him $600" were (or should it be "is", or, perhaps "was"?) correct or not, but @kiamlaluno objected that the grammatical version of the above sentence is, or would be, "He is demanding that my father pays him $600".

Please, note the italicized pays, which, I think, kiamlaluno aseptically used in reference to the third person "father".

Answering the question, another user, @Jay, presumably a native speaker, wrote 'a more common wording would be […] "He is demanding that my father pay him $600"'.

Being an Italian speaker, and, as such, particularly aware about the difference between "indicative" and "subjunctive" moods, I don't think Jay randomly used "pay" rather than "pays", as Kiamlaluno did.

So, I think that "pay" is correctly used in the subjunctive form there, whereas "pays" is wrong because it doesn't render the involved meanig of the sentence.

Am I wrong in asserting what above? If so, why?

Best Answer

As so often, Swan in Practical English Usage (p541) has a good explanation:

The subjunctive is a special kind of present tense which has no -s in the third person singular. It is sometimes used in that-clauses in a formal style, especially in American English, after words which express the idea that something is important or desirable ... .

So whether you use pay or pays here has nothing to do with time but is about formality. It is more likely that an American native speaker than a British native speaker will think you are making a mistake if you use the indicative (with -s) rather than the subjunctive (without -s).