Grammatically Correct: The writer's essential guide to punctuation ...

Problem Category 2:
Forest or Trees?
This section describes scenarios where writers often mistake a
singular subject for a plural one or vice versa, and hence match the
wrong verb to it.
COLLECTIVE NOUNS
A collective noun refers to an entity made up of more than one
thing or person: crowd, government, flock. Whether such a word
functions as a singular or a plural depends on several factors.
SOME ARE ALWAYS SINGULAR OR ALWAYS PLURAL
The mob was turning ugly.
A mob is treated as a unit, since by definition the people who
make it up could not individually exhibit mob traits.
The supplies were running low.
You can have a supply of something, but when the reference is
to provisions, this word is always plural.
Where are the binoculars?
Items that are made up of two connected parts often take a plural
construction-scissors, slacks, glasses, pants, pliers. They are only
properly used as singulars if preceded by the phrase a pair of
SOME ARE SINGULAR WHEN USED IN ONE
SENSE, AND PLURAL IN ANOTHER
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The new headquarters are in Paris.
[the physical entity]