that is used as an essential modifier [Essential modifier: a modifier without which a sentence/intent of a sentence is incomplete]

Essential Modifier example:
When Congress reconvenes, some newly elected members from rural states will try to establish tighter restrictions for the amount of grain THAT farmers are allowed to grow.
Explanation SC way:
', WHICH' should not be used in place of THAT. The author of the sentence intended that the amount of grain be the same amount that the farmers are usually allowed to use. Thus 'farmers are allowed to grow' is an essential part of the sentence.

Explanation PS way:
In the above sentence we are talking about:
Establishing restriction for X.
Let
A= amount of grain
B = grain used by farmers
Then X=AB
and not AB, or A itself

Uses of that as a modifier:
When you need to modify an thing(s)/animals
Narrows the identity of the thing(s)/animals
Cannot be logically removed

When not to use that:
When the modifier is enclosed in a comma (,)
To modify places/person (Use Where to modify places, who to modify persons, whom to modify possessives)

zaaash wrote:that is used as an essential modifier [Essential modifier: a modifier without which a sentence/intent of a sentence is incomplete]

Essential Modifier example:
When Congress reconvenes, some newly elected members from rural states will try to establish tighter restrictions for the amount of grain THAT farmers are allowed to grow.
Explanation SC way:
', WHICH' should not be used in place of THAT. The author of the sentence intended that the amount of grain be the same amount that the farmers are usually allowed to use. Thus 'farmers are allowed to grow' is an essential part of the sentence.

Explanation PS way:
In the above sentence we are talking about:
Establishing restriction for X.
Let
A= amount of grain
B = grain used by farmers
Then X=AB
and not AB, or A itself

Uses of that as a modifier:
When you need to modify an thing(s)/animals
Narrows the identity of the thing(s)/animals
Cannot be logically removed

When not to use that:
When the modifier is enclosed in a comma (,)
To modify places/person (Use Where to modify places, who to modify persons, whom to modify possessives)

I am specifically interested in the last part of the explanation that deals with when "that" can be ignored. In the sentence under discussion, there is no comma after 'amount of grain', still 'that' is ignored. Can we generalize when 'that' can be ignored, though there is no comma after the noun.