When we speak of nouns as being countable or uncountable, we
mean that some things can be counted while others cannot.
Countable nouns name individual items that can addup; there can
be one or more of them.  Other things cannot be counted; they
are considered collective rather than individual items.  In many
cases this distinction is easy tonunderstand.  We all
recognize that we can count items like books, tables, eggs, or mountains.
We can easily imagine one or more of such items.  And most of us
recognize that it is not possible to count other things like
water, dust, air, or ice cream.  These things cannot easily be
separated into individual items.  

     But many nouns are uncountable for less obvious reasons. 
Most concepts or abstract ideas like peace, happiness, wealth and
knowledge are uncountable.  So are many activities such as
swimming, eating, and debauchery, and some conditions such as
confusion, frustration, satisfaction, and certainty. These nouns
are considered uncountable because they are not easily identified
as single things--the idea of happiness can consist of many
different things and can be different for different people--or
because they refer to general activities rather than specific
instances; eating refers to the activity in general, not any
particular example.  The names of most disciplines are also
uncountable, for example, sociology, medicine, anthropology. 
Nouns ending in -ism are also usually uncountable, for example,
feminism, optimism, patriotism. 

     Some uncountable nouns like money, homework, work, and
gossip are very confusing for learners of English because they
seem to refer to particular items, yet they are treated as
general.  When we speak of work, we are not thinking of a
particular job or activity--we include the idea of what anyone
might do in any job that would be considered doing work.  Jobs
are countable items that are specific instances of the general
idea of work.  
     In the same way, homework is not the particular assignment
or assignments a student does. It is the general idea of students
doing assignments.  When a student says, "I have to do my
homework," he or she may mean one assignment or several
assignments or parts of one or more assignments, so the student
knows what particular activities are involved, but they are
referred to as part of a generalized activity--my homework can be
something different every day.  
     

***Note: As you have perhaps noticed, individual activities like
jobs and assignments--which are closely identified with
uncountable nouns like work and homework--are countable.  That
means that although you can't say "I have lots of homeworks to
do," you can say "I have lots of assignments." 

     Money is an interesting example of an uncountable noun
because, of course, lots of people love to count their money.  

     Also confusing for many students are the numerous English
nouns that have both a countable and an uncountable sense. 
Depending on the context, these nouns sometimes refer to a
particular thing and at other times to a general idea.  In some
cases this is not difficult.  
For example, 
     Death (in general) is inevitable.
     She missed work because there was a death in her family.
However, many nouns are thought of as general more by custom than
for any clear reason.  Many food items fall into this category,
e.g., chicken, cheese, and fruit.
     Thus, we see a chicken on a farm, but we eat chicken; we say
that the tomato is a fruit, not a vegetable, but we like fruit on
our cereal.  

**Note: individual servings of food items are usually countable,
but not the food itself, e.g.,
     
               pie            a piece of pie
               bread          a slice of bread    
               gum            a stick of gum 

     Other nouns that can be either countable or uncountable
include substances that things can be made of, like paper or
glass.  When you write an essay on paper, it becomes a paper.  
Other nouns in this category are words like wood and cloth, which
refer to the material that may be made of many different
varieties of tree or fabric.  Thus, the material of an elm, an
oak or a pine is all wood and linen, silk and cotton are all made
into cloth. 

                  Some Common Uncountable Nouns

accuracy       darkness       fun            inferiority
admiration     economics      furniture      information
advice         efficieny      garbage        integration
aggression     electricity    generosity     intelligence
air            enjoyment      gravity        irritability
assistance     entertainment  happiness      isolation
behavior       estimation     health         junk
boredom        equipment      heat           justice
bravery        evidence       help           knowledge
chemistry      evolution      homework       laughter
clothing       excitement     honesty        leisure
comprehension  fame           ignorance      literature
courage        foolishness    immigration    luck
luggage        peace          recreation     stuff     
machinery      permission     relaxation     superiority
mail           physics        reliability    survival
math           poetry         research       tolerance
merchandise    pollution      sadness        traffic
money          poverty        safety         transportation
music          pride          scenery        trouble
news           productivity   shopping       violence
nonsense       progress       significance   water
oxygen         propaganda     slang          wealth
participation  psychology     snow           weather
pay            rain           status         wisdom
               


     Some Nouns that can be either Countable or Uncountable      
     


abuse          drama          jail           reading             
adulthood      duck           jealousy       religion
afternoon      education      language       revision
age            environment    law            rock
anger          evening        liberty        science
appearance     exercise       life           school
art            fact           love           shock
beauty         faith          lunch          society
beer           fear           man            sorrow
belief         fiction        marriage       space
breakfast      film           meat           speech
cheese         fish           metal          spirit
chicken        flavor         milk           stone
childhood      food           morning        strength
cloth          freedom        murder         surprise
college        friendship     nature         teaching
commitment     fruit          paper          temptation
competition    glass          passion        theater
concern        government     people         theory
crime          hair           personality    time
culture        hatred         philosophy     tradition
death          history        pleasure       trouble
desire         home           power          truth
dinner         hope           prejudice      turkey
disappointment ideology       pressure       understanding
discrimination imagination    prison         weakness
disease        injustice      punishment     wine
divorce        innocence      race           writing


     There are, of course, many additional uncountable nouns in
English.  If you are unsure of any particular noun, you can use a
dictionary for learners of English.  For instance, both Longman's
Dictionary of American English and Longman's Dictionary of
Contemporary English use the symbols [C] and [U] to identify
countable and uncountable nouns.