How can I determine subject or object in the sentence, when I use clauses?

[Dammam1983]

How can I determine subject or object in the sentence ,especially , when I use clauses.

E.G.

1-When which, who and that are subjects, like this:
We can shorten them like this:
Those are the traineeswho study in this building.

2-When which, who and that are objects, like this:
We can shorten them like this:
Cereals are a family of plants which we use for food.

My QUESTION IS . How can I determine Subject Or Object

[Everafter]

We determine them through the meaning of the sentence and the position, too.

**Those are the trainees who study in this building.
We can't shorten the sentence above as the relative clause is a subject and necessary for the meaning.
......................................................
Cereals are a family of plants which we use for food.

This can be shorten : Cereals are a family of plants used for food.

The relative clause is an object and we omitted it.

[Cerberus™]

In the first sentence, you could ask:
- Who or what is it that studies? - The trainees.
Since you know "trainees" is the antecedent of "who" (the word that "who" refers to), you know that "who" must be subject in the relative clause. Moreover, if "who" were not subject, there would be no other word that could be the subject of "study", which is impossible.

In the second clause, you could ask:
- Who or what is it that uses? - We.
Then you know "we" is subject. Next you could ask:
- Who or what do we use? - Plants.
Since "plants" is the antecedent of "which", "which" must be object. Moreover, "we" can never be object, or it would be "us".

Everafter: you could shorten "those are the trainees who study in this building" as "those are the trainees studying in this building": I'm not sure what you mean by this. Perhaps you mean that, if you can shorten a relative clause into a past participle, the relative pronoun must have been object, since the past participle is passive and goes with what used to be the object?

[David30]

Hi,
All sentences containing relative clauses can be shortened.
Is it true?
Thanks

[Mister Micawber]

I doubt it, David, if the meaning is to be maintained, but I am willing to try shortening any sentences you provide.
_________________
Native English teacher at Mister Micawber's

[David30]

Thanks Mister Micawber
The quiz page, http://www.mistermicawbers.com/index.php?p=1_2_Quizzes , is very interesting and contains many information.How do I check my answers?
Happy Christmas

[Mister Micawber]

Hey, David-- thanks for finding me! Those pages are designed for my own students here in Yokohama, Japan, and we discuss the quizzes and jokes in class, but if you PM me with your answers, I will be delighted to check them for you.

MM
_________________
Native English teacher at Mister Micawber's

[David30]

Thanks Mister Micawber

[Dammam1983]

Thank you so much,

I really appreciate what you have done

Best regards