Common Errors: modifiers
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A pronoun must refer to a single noun, not a phrase or a collection of oddments and especially may not refer to nothing at all. Check your work to determine the reference for pronouns.
The accountant's wheelbarrow was full of eels, which irritated the fastidious spectator.
The which does not refer to a specific noun.
The presence of eels in the accountant's wheelbarrow irritated the fastidious spectator.
Modifying phrases must modify something appropriate. "Misplaced" modifiers dangle about untidily.
Here are some examples.
While climbing Mt. Kilimanjaro, which is quite steep up to the very top and then slopes away rather sharply, Rupert's hair dryer required constant adjustment.
(Who is climbing the mountain? The hair drier?)
Ducking under a flock of pestilent soiled budgies, the handlebars struck the sandwich in my pocket doing irreparable harm to the avocado.
(Who or what is ducking?)
To Rupert's surprise, he was comfortably able to drive the tractor wearing swim fins and goggles.
(Is the tractor wearing swim fins and goggles?)
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Excerpted with permission from SAT Practice: The New Verbal Section.