Take the 2-minute tour ×
English Language & Usage Stack Exchange is a question and answer site for linguists, etymologists, and serious English language enthusiasts. It's 100% free, no registration required.

Sometimes, the word 'that' to introduce a dependent clause is optional. For example, these sentences both make sense with or without 'that':

Long books [that] religious people like tend to be Bibles.

Water tanks [that] fish need are spacious.

... whereas in these sentences, 'that' is mandatory and the sentence is ungrammatical without it:

Those that are rotten must be thrown away.

Cars that break down endanger pedestrians.

I can't quite put my finger on the rule which determines when 'that' must be used. What is it?

share|improve this question
2  
I noticed right away that in your last two examples, "that" is followed by a verb, which is not the case with the first two. –  KitFox Jul 25 '11 at 17:55
1  
Related: Use of "that" in a sentence. –  kiamlaluno Jul 25 '11 at 18:26
    
Embedded clause or dependent clause? –  Peter Mortensen Jul 27 '11 at 8:26
add comment

1 Answer 1

up vote 10 down vote accepted

In both of the examples in which that is optional, the relative pronoun is the object of the embedded clause.

Long books [that] religious people like tend to be Bibles. [Religious people like long books.]

Water tanks [that] fish need are spacious. [Fish need water tanks.]

In your other examples, the relative pronoun is the subject of the embedded clause:

Those that are rotten must be thrown away. [Those are rotten.]

Cars that break down endanger pedestrians. [Cars break down.]

English only allows you to omit that when it has been moved from the object position of the embedded clause. I suspect that the reason for this is the ease of comprehension on the part of the listener. A sentence like Cars break down endanger pedestrians, if it were grammatical, would be extremely hard to parse.

share|improve this answer
1  
+1 for illuminating clarity –  FumbleFingers Jul 25 '11 at 18:13
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.