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nouns
4.3  Types of Nouns
common vs. proper

COMMON: definite form vs. indefinite form, countable vs. uncountable

4.3.2.1. Countable vs. uncountable uses of nouns

4.4. Determiners
articles=1 kind of central determiner
4.4.1 definite vs. indefinite articles
1.1 Indefinite + singular countable
a frog
1.2 zero article + uncountable and plural countable
frogs, frog
1.3 Definite + countable, uncountable
the frog, the frogs
1.4 Generic reference
frogs 
a frog
the frog