we are free to use whichever model is most convenient

[GoodTaste]

But there may be many different ways in which one could model the same physical situation, with each employing different fundamental elements and concepts. If two such physical theories or models accurately predict the same events, one cannot be said to be more real than the other; rather, we are free to use whichever model is most convenient.

Source: The Grand Design by Stephen Hawking

It seems to me there is something missing or omitted in the sentence "we are free to use whichever model is most convenient".
Should it be "we are free to use whichever model that is most convenient" or "we are free to use whichever model which is most convenient", because the object is
"whichever model", not "whichever model is most convinent".
But if "that" or "which" is omittable, it will be okay.
Yet it doesn't appear omittable to me eccept "which", which is very close to "whichever" and might be omittable here. I am not sure.

Is the sentence okay?

 

[Barque]

It seems to me there is something missing or omitted in the sentence "we are free to use whichever model is most convenient".

The phrase is perfectly fine (it isn't a sentence here but a part of one). There is nothing omitted or missing because the word "whichever" acts as an adequate qualifier. Adding "which" or "that" would be redundant and ungrammatical.

 

[dunchee]

because the object is
"whichever model", not "whichever model is most convinent".

As a matter of fact, the object of use is "whichever model is most convenient."

Practical English Usage by Michael Swan, 3rd ed
625 whoever, whatever etc
3 clauses as subjects or objects
A clause with … whichever … can be the … object of the verb in the other clause.

I'll take whichever tent you're not using. (object of take)​

 

[GoodTaste]

I'll take whichever tent you're not using. (object of take)

Taking you out, is it still natural? When the situation is applied to the OP, a problem will be produced. Native speakers appear to be used to the grammatical structure, but unable to clearly explain why.

See?
I'll take whichever tent is not using.

Can you announce that the above sentence is correct?

 

[5jj]

It is incorrect.

 

[jutfrank]

It seems to me there is something missing or omitted in the sentence "we are free to use whichever model is most convenient".

I think I see why.

Should it be "we are free to use whichever model that is most convenient" or "we are free to use whichever model which is most convenient", because the object is "whichever model", not "whichever model is most convinent".

No, the object isn't whichever model. The whole phrase whichever model is most convenient is a clause in itself acting as complement of use. The subject of the clause is whichever model.

Taking you out, is it still natural? When the situation is applied to the OP, a problem will be produced. Native speakers appear to be used to the grammatical structure, but unable to clearly explain why.

In the clause whichever tent you're not using, the phrase whichever tent is functioning as an object of using, not a subject. If you remove the subject you, it doesn't make sense.

I'll take whichever tent is not using.

That sentence is wrong because it doesn't make sense to have whichever tent as the subject of using.

 

[GoodTaste]

But if the sentence is:

I'll take whichever tent is not being used.

Is it correct?

 

[Tarheel]

Yes.