There are certain situations where nouns do not require any kind of article (definite or indefinite) before them. Such instances are discussed below- 

If proper or abstract uncountable noun is used in general sense, article need not to be used before the noun. e.g.

  • Diamond is an expensive material. 
  • Knowledge is the power.
  • Calcutta is known as the city of joy. 

Article is not put before plural countable nouns which are used in general sense. e.g.

  • Children are innocent. 
  • Dogs are faithful animal. 

No article is used before language, country, names of days and months. e.g.

  • Mount Everest is located in the Mahalangur Himal sub-range of the Himalayas. 
  • December has 31 days. 
  • He speaks in English.