Fewer Puppies-Less Poop (fewer and less, amount and number)

As the owner (mother, really) of two Jack Russell terriers who use a litter box,
I'm definitely qualified to talk about poop. Today our topic is the difference
between "fewer" and "less," which will be studied with "amount" and "number."

Before I begin, I'd like to call your attention to an addition I made to the
post "If I Were a Rich Man," which I hope will help to clarify the concept of grammatical mood. (Sometimes I add to earlier posts when ideas occur to me.)

We'll start with the concepts of amount and number.

The word "amount" refers to mass or quantity. It is used with things that are measured in bulk and cannot be counted in units. We use it with things such as these: bread, cheese, milk, rainfall, happiness, evidence, news, and
information, but it should NEVER be used with items that can be counted individually. It is INCORRECT to say that a large AMOUNT of people attended a concert; instead say a large NUMBER of people attended. The word "amount" is often followed by the preposition "of" before a singular noun, and it always takes a singular verb. (A large amount IS, not ARE...) The following sentences use "amount'" correctly:
           The amount of support he received astonished him.
           After the storm, a large amount of debris littered the streets.

The word "number" is used with items that can be counted, and it is followed by
a plural noun, naming persons, places, or things which are discrete and separable units.

The verb that follows "number" can be singular or plural. When the sentence
refers to the number itself, taken as a unit, and not to individuals being counted, the verb is singular. In such sentences, the word "number" is preceded by the definite article, "the."
These sentences use "number" followed by a singular verb:
            The number of applicants IS increasing.
            What IS the number of absent students?
 
After an indefinite article, "a" or "an," the word "number" refers to individual units and takes a plural verb. In the following sentences, "number" is used correctly:
             A number of the books ARE lost.
             An enormous number of homes HAVE been damaged by the flood.

Each of these sentences uses "amount" and "number" correctly:
            The NUMBER of calls we received reflects the AMOUNT of interest in
                 our plan.
             We'll have to buy a large AMOUNT of food for that NUMBER of guests.
             The NUMBER of coins she collected was worth a large AMOUNT of
                 money.
             The large NUMBER of acres that are burning requires a greater
                 AMOUNT of water.                                                                                 
In the above sentences, you can see that "amount" tells us how much, and "number" tells us how many.

These adjectives are used to describe "amount" and "number":
                               amount                                      number
                                 little                                           few
                                 less                                           fewer
                                 much                                         many
                                 more                                          more

In the above columns, notice that "fewer" is listed under "number." It is the comparative degree of the adjective "few," and, like "number," it is used with persons, places, and things that can be counted. "Fewer" modifies nouns that are plural.
Here are some sentences in which "fewer" is used correctly:
          Fewer than four boys arrived for practice.
          Fewer than twenty people responded to our email.
          We were disappointed to hear that fewer than five of us would be
             accepted.
          I lost fewer pounds on this diet than on the other one.
          My house has fewer square feet than yours.
          My new job has fewer days of vacation than my old job did.
          Do these cookies have fewer calories than those?

In the chart showing the adjectives that go with "amount" and "number," notice
that "less" is listed under "amount," in line with "fewer." It is the comparative degree of "little," and, unlike "fewer," it can be an adverb as well as an adjective. "Less" refers to degree, extent, or amount, and it modifies singular nouns that name uncountable things, such as luggage, furniture, courage, corn, excitement, paper, and supervision. Singular nouns preceded by "a" or "an" will not take "less." It uses a singular verb.
The following sentences use "less" correctly:
            This recipe is better for diabetics because it requires less sugar.
            The meteorologist forecasts less precipitation this winter.
            Did your doctor recommend that you eat less salt? 
            Newer appliances consume less energy than the older ones.

These statements show the difference between "fewer" and "less":
           1. Fewer" refers to a smaller number, and "less" refers to a smaller
                   amount.
           2. Less" means "not as much," and 'fewer" means "not as many."
           3. If you can count individual items, use "fewer," and if you can't,
                   use "less."

An AMOUNT of something can consist of a NUMBER of individual units, so you can have LESS of the amount and FEWER of the units, as in:
          LESS time, FEWER hours         LESS money, FEWER quarters
          LESS work, FEWER jobs          LESS candy, FEWER jelly beans
          LESS tonnage, FEWER ships   LESS manpower, FEWER men
          LESS light, FEWER bulbs         LESS postage, FEWER stamps
          LESS travel, FEWER trips         LESS laughter, FEWER laughs

Each of the following sentences uses "fewer' and "less" correctly:
             LESS effort was exerted, so FEWER results were achieved.
             She's trying to eat FEWER chips and drink LESS soda.
             The LESS money you have in your account, the FEWER
                 unnecessary purchases you should make.
             We had FEWER school cancellations this year because there was LESS
                 snow.
              She lost weight because she consumed LESS fat and FEWER calories.

In general, it's true that "less" is used only with singular nouns, but there is an exception: references to units of time, weight, distance, measurement, and
money, which are treated as amounts and not as individual counted units.
In these situations the plural noun is regarded as a single entity. "Less" is also
used with numbers used alone and with mathematical statements.
Here are some examples:
     less than an hour                less than five dollars       less than $100
     less than three miles           less than two minutes     less than twelve years old
     less than two cups of flour  less than two years ago  less than 2/3 of the vote
     less than 20 percent           less than five pounds      less than ten yards
                                                 4 is less than 8
                       
                                                                                            
P.S. The supermarket sign "10 Items or Less" is incorrect.
P.P.S. Don't forget that "fewer in number" is redundant.