Theory:

There are five classifications of common nouns:
  1. Countable nouns
  2. Uncountable nouns
  3. Collective nouns
  4. Concrete nouns
  5. Abstract nouns
Countable nouns can be both singular and plural. They are distinct units that are easily numbered.
Example:
1. four dogs
2. twenty miles
3. two apples
Uncountable nouns, also called non-countable nouns, are singular only. You cannot use "a" or "an" with them
Example:
1. water
2. air
3. grass
Collective nouns represent a group of things. The singular form refers to one unit or group, and the plural form refers to more than one unit or group.
Example:
1. class
2. department
3. family
Concrete nouns represent something physical that can be experienced through the senses. These nouns can be tasted, touched, seen, heard or smelled. They can be common, proper, singular, plural, countable, uncountable or collective.
Example:
1. cheese
2. computer
3. flower
Abstract nouns refer to things that aren't concrete. They cannot be seen, touched, heard, smelled or tasted. They refer to emotions, ideas, concepts, traits, experiences or states of being.
Example:
1. culture
2. peace
3. sympathy