Using "that" within a sentence

[Chamara Janaka]

I heard the following sentence in a movie but I'm not sure whether I didn't hear the word "that" or it's not necessary in the context.

Have you written the essay I gave you yesterday?

Have you written the essay that I gave you yesterday?

 

[Raymott]

I'm not sure whether you heard it either. It is not necessary to use there; it's optional. Either way, it's right. You will find many examples of this (leaving out 'that').

 

[MikeNewYork]

In many cases, "that" is optional in a relative clause unless it is the subject of the clause.

 

[Rover_KE]

I agree with Mike.

An example of that, Chamara Janaka, would be

'Have you finished the essay that was due yesterday?' (You can't omit 'that'.)

 

[emsr2d2]

True, but you can omit "that was".

Have you finished the essay due yesterday?

 

[moemenkhallaf]

True, but you can omit "that was".

Have you finished the essay due yesterday?

Why we cannot omit "that" but we can omit "that was" ?

 

[Raymott]

Why can't we [STRIKE]cannot [/STRIKE]omit "that" but we can omit "that was" ?

"Have you finished the essay due yesterday?"
For the same reason we can omit "the essay due yesterday", but not "the essay" in the above. It's not so much about what you omit, but whether what you leave behind makes sense or not. In this case, omitting "that was" leaves a proper sentence behind. Omitting "that" does not.

 

[5jj]

Why we cannot omit "that" but we can omit "that was" ?

You need to say either "Why can't we omit ...?" or, more formally, "Why can we not omit ...?"