It is said that we cannot use articles with "abstract nouns". But here articles are used with them? I am just confused. How do you explain this in detail?
- Don't tell a lie.
- Speak the truth.
- I have a headache.
None of the nouns in your examples are what people mean when they speak of "abstract nouns".
An abstract noun designates a quality or "essence" abstracted—"taken away from"—any concrete instance. Beauty, for instance, is the quality we attribute to beautiful things, and Nobility is the quality we attribute to noble people; but we use them as abstract nouns only when we consider them as having some sort of existence apart from beautiful things and noble people.
But the words we use to designate these abstract qualities can also be used to designate instances of the qualities occurring. The beauty of nature is not wholly abstract beauty but the particular beauty we find in nature. We say that a man or woman exhibits a certain nobility on a particular occasion or in a particular action.
In your examples,
Lie is never an abstraction; a lie is an untrue statement.
Headache is never an abstraction; it may designate a condition suffered by a particular individual (I have a headache) or it may be employed as a designation for the condition considered under the aspect of etiology or treatment (Headache may be treated with aspirin).
Truth may be an abstraction (Beauty is Truth, Truth Beauty, that is all You know on earth and all you need to know), but in Tell the truth it means not the abstraction but a statement to which truth may be attributed, a true statement.
I think it is simply idiomatic, which makes it hard to understand.
We say, "I have a headache" and "I have a medical condition," but "I have shingles," and "I have heartburn."
We say, "Speak [or Tell] the truth," but "This is a truth worth knowing," or "There is no truth in what you say."
We say, "Don't tell a lie," but "That was untruthful," or "Your lie hurt my feelings."
These are examples of why English is so difficult to learn!
To quote from part of @rogermue's answer (linked in the comments below):
"A better formulation of the rule would be 'Abstract nouns are mostly used without articles, but there are cases where an article is used.' It is impossible for grammars to cover a lot of grammar points with exact rules. The handling of such 'grey' grammar zones is a matter of experience you only get by reading a lot of original texts."
Some abstract nouns can be used in a particular sense with a/an, but in the singular only:
So, may be 'lie' come with 'a' article (according to 'A Practical English Grammar')
I have its answer. It is very hard to understand the rules of English Grammar, In the Sentence "Tell a lie" lie is a singular noun and it's also a rule to use "A" before singular noun for e.g. a one rupee note. And with this, there is also a rule for it , that we use article "A" only with countable nouns and we can count our lies but we can't count our truth that is the reason to use A with Lie and The with Truth.