Why does Ruby use respond_to? instead of responds_to?
Matz prefers second person singular or third person plural:
"responds_to?" probably makes more sense to English speakers than "respond_to?".
Maybe. But I'm Japanese. Ruby is not English. It's the basic naming rule to avoid third person singular form in the standard libraries.
you = Human.new if you.respond_to?(:knock) ... end
How do you know that the receiver is always third person singular? It is possible that the receiver be I, we, you, or they, or some other thing that represents plurality. In that case, will you still say that responds_to? is more natural than respond_to?? In order to preserve generality, it is better to name a method in a form as general as possible. Rather than naming a method in third person singular, it makes more sense to name it in the default, to-less infinitive form, which is also used in dictionaries.