The running boy is my son.
I have troubles in how to use pre-noun present participles (i.e., ing) in English. How do you find a sentence like "The running boy is my son"? Can it mean "The boy, who is now running, is my son"?
That's close. If you remove the commas before "who" and after "running", then I would consider it to be equivalent. It's difficult to explain why, but it's the difference between a restrictive (without commas) and non-restrictive (with commas) clause. In speech, the commas would be indicated by pauses.
"The boy, who is now running, is my son." This means, "The boy is my son. By the way, he is now running." In this case, the listener already knows which boy is being talked about, whether or not the non-restrictive clause "who is now running" is present.
"The boy who is now running is my son." This means that the particular boy who is running is the speaker's son, and not any of the other boys who might be present. This is what "The running boy is my son" means. It may help to think of "running" as an adjective in this context: it's the same idea as "The tall boy is my son", except we're describing an action that the boy is doing instead of one of his basic characteristic. The listener might not know which boy is being talked about without the restrictive clause.
Does that make sense? :)
やっぱり! Even before I opened this topic, I thought this was Japanese-English. Yes, you can say "The running boy is my son", but it doesn't sound natural to me. It sounds like a copy of what one might say in Japanese. I'd say this: The boy (who is )running is my son.
Reminds me of something parents would say at a Sports Day Meet in Japan.
BTW, Taro-san, ne, did you write that explanation in Japanese about fit and fitted?
"The running boy is my son" is odd? how? I don't c it.
Even though it's clear from context here that the boy is running (part. adj.), it can also be interpreted as "The running boy (i.e. running-boy) is my son" where running is a noun rather than an adjective (cf. 'driving school', 'dining hall' , 'batting practice', etc.). This is one of many ambiguities of Modern English.
The best known example is the sentence: "Pursuing girls can be fun."
Does the speaker mean: "The pursuit of girls can be fun" or "Girls who pursue can be fun"?