Noun Modifiers: comma + which

[EmmaL654]

With reference to P54, All the Verbal, when more than one noun modifiers are in place, an essential modifier takes precedence over a nonessential modifier:

The BOX of nails, which is nearly full, belongs to Jean.

How do I tell the comma + which modifier isn't referring to "nails" the, quote, "very nearby noun" (Page 53), unquote?

It appears to me that the two grammatical rules conflict with each other sometimes. Is there a grammatical explanation for this example?

[esledge]

First, please accept our apologies for the late response. A tech glitch has hidden this folder from all logged-in Manhattan Prep staff since the New Year, so I didn’t see this question until now.
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How do I tell the comma + which modifier isn't referring to "nails" the, quote, "very nearby noun" (Page 53), unquote?

It appears to me that the two grammatical rules conflict with each other sometimes. Is there a grammatical explanation for this example?

In this one, meaning plays a primary role: "nails" cannot be "nearly full," but a "box" can be. Skipping over "of nails" to make the "box..., which" connection is thus logically sensible. The point of this example is that grammatically, you have several excuses for putting "of nails" in the middle:
1) It's not misleading (as noted above, about the meaning)
2) It's short (just 2 words)
3) It's necessary (without "of nails," we wouldn't know what box it is, or what it is nearly full of)

The situations you would avoid on the GMAT violate all or any of the three list items above.

WRONG: The farm, owned and operated by the family for several generations, which produces fruit and nuts for the nation, is situated in the fertile valley.

In this example, the modifiers between the "which" and the intended noun are:
1) Misleading: "generations...which produces" could be the interpretation, but it has subject verb disagreement. Then again, "the family..., which produces" or "the farm..., which produces" could be the interpretation. This uncertainty is not acceptable on the GMAT.
2) Very long: Anything longer than about 5 words is probably too long between "which" and the intended noun.
3) Not necessary (it's nice to know that the farm is "owned and operated by the family for several generations," but that fact does not identify the specific farm, and should be placed elsewhere in the sentence (especially since it can be).

RIGHT: Owned and operated by the family for several generations, the farm, which produces fruit and nuts for the nation, is situated in the fertile valley.