usage of indefinite vs. definite articles with nouns denoting a class

[vgv888888]

[1, p.5] tells that "Singular Nouns denoting a class" are prepended by the definite article "THE" (Example: **"The Cobra is dangerous"**) while [1, p.7] tells that "Singular countable nouns denoting a class" are prepended by indefinite articles ("An elephant never forgets")

I could not get what is the difference between two cases mentioned?
Why cannot I write according the same rules "A Cobra never forgets" and "The elephant is dangerous"?

[1]
PRACTICAL REALISATIONS OF ENGLISH DEFINITE AND INDEFINITE ARTICLES
search internet for the pdf with this title, I cannot post any links yet

[lauralie2]

More clearly,

When preceded by the, a singular countable noun can be used to represent something as a class.

e.g. The telephone is a modern convenience.
The horse is a domesticated animal.
The eagle is a bird of prey.

In the first example, the telephone refers to telephones considered as a class. Likewise, in the other examples, the horse refers to horses considered as a class, and the eagle refers to eagles considered as a class.


A is referred to as the indefinite article because it can be used to refer to something in general terms. A and an are often used in general statements.

e.g. A bank account can provide a good means of saving money.

An accountant must have a good knowledge of arithmetic.

A good pair of scissors should be used for cutting cloth.

Source

Note,

• The cobra is dangerous. <class>
• A cobra is dangerous. <general statement>
• An elephant never forgets. <general statement>
• The elephant never forgets. <class>

[vgv8]

A is referred to as the indefinite article because it can be used to refer to something in general terms. A and an are often used in general statements

How does it relate to the rule(?):

• DO NOT use an article when you are speaking about things in general
  I like Russian tea.
  She likes reading books.

Also, specified in cited originally [1] as articles "Omissions" case of "Abstract nouns"

[lauralie2]

How does it relate to the rule(?):

• DO NOT use an article when you are speaking about things in general
  I like Russian tea.
  She likes reading books.

Also, specified in cited originally [1] as articles "Omissions" case of "Abstract nouns"

It wouldn't relate to 'tea', a non-count noun, or 'books', a plural noun.

Indefinite 'a/an' modifies a singular countable noun:

• a bank account
  
  • 'a' goes with 'account', a singular countable noun, not 'bank', an adjective.
• an accountant
  
  • 'an' goes with 'accountant', a singular countable noun.
• a good pair of scissors
  
  • 'a' goes with 'pair', a singular countable noun, not 'good', an adjective.

[vgv8]

Thanks for your patience, lauralie2,

• The cobra is dangerous. <class>
• A cobra is dangerous. <general statement>
• An elephant never forgets. <general statement>
• The elephant never forgets. <class>

What would

• 
  "Curiosity killed the cat, but satisfaction brought it back."
  (zero article instead of "the")
• 
  "Curiosity killed the A cat, but satisfaction brought it back."
  ("the" --> "A")

mean?

What would "

• "An apple a day keeps the doctor away"
  (zero article instead of "the")
• "An apple a day keeps the A doctor away"
  (indefinite article instead of "the")

mean?

[vgv8]

It wouldn't relate to 'tea', a non-count noun, or 'books', a plural noun.

Indefinite 'a/an' modifies a singular countable noun:

Well, examples (with uncountable indefinite or plural indefinte) were (not mine but included with from cited reference) completely out of context (relating really to another rule) and so misled and ambiguated that rule.

Does the rule:

• DO NOT use an article when you are speaking about things in general

apply to countable nouns (either singles or plurals, either indefinite or indefinite)?

[lauralie2]

Thanks for your patience, lauralie2

You're most welcome.

The following are fixed saying:

1. Curiosity killed the cat.
2. An apple a day keeps the doctor away.

Changing the article results in,

1a. Curiosity killed cat.
2a. An apple a day keeps doctor away.

1a. and 2a. are ungrammatical because singular count nouns need an article.

1b. Curiosity killed a cat.
2b. An apple a day keeps a doctor away.