A, An and The are called Articles.
**NOTE: Formerly articles were classed as a separate part of speech; but now they are classed as adjective.
01. A and an are called Indefinite Articles, because they do not point out any particular person or thing: a book =any book, a girl = any girl.
**NOTE: An is really the weakened form of one and a is formed from it simply dropping the letter n.
02. “The” is called the Definite Article, because it points to some particular person or thing: the boy= the boy of whom we are speaking or who is known.
03. As a general rule, a Common Noun in the singular number should have an article before it. Thus, we cannot say, “I have seen tiger" we should say, “I have seen a or the tiger."
But a Common Noun in the plural does not require the unless we want to particularize: Boys love games. But, the boys (those already referred to, or those before us) are playing.
04. ‘A’ is used before
a) Consonants: a boy, a word, a B. A.
b) Such vowels as have the sound of ‘yu’: aewe, a useful thing, a unit, a European, a university, etc.
c) ‘O’ when it is sounded as in ‘one’: such a one, a one taka-note, etc.
05. ‘An’ is used before
a) A vowel: an eye, an idiot, an ox, etc.
b) Consonants beginning with a vowel sound: an M.A.; an M. d., an heir, an honest boy, an hour.
c) Aspirated h, when the accent is on the second syllable: an hotel. Some other words of this class are: habitual, harmonious, heraldic, heroic, heretical, hypothesis.
**NOTE: But, according to Fowler (Dictionary of Modern English Usage) “An was formerly used before an unaccented syllable beginning with h (an historical work); but now that the h is sounded the distinction has become pedantic, and historical should be said and written.”
06. The position of ‘A’ or ‘Am’:
“When there is also another adj.., or adv.., and adj.., a or an precedes it or them: but is follows many, such, what (exclamation) etc. and adjective proceeded by how, so, as or too: what a blessing! Many a long day, how different a fate! too serious a matter and is usually placed between quite and rather and their adjectives, as quite a good hat, rather a quiet fellow.”--Pocket Oxford.
07. a) Generalizing ‘A’ or ‘An’-- A or An is sometimes used before a noun to indicate a class. It is then called the Generalizing ‘A’ or ‘An’: A son should obey his father. An ant is an industrious creature.
b) A used as a Preposition-- He went a-hunting (=on hunting). Rice sells half a seer a (per) taka.
08. Rules for the use of ‘The’
The is used before:
a) The name of rivers (the Hudson River), gulfs (the Persian Gulf), seas (the Black Sea). Mountain ranges (the Himalayas), groups of islands (the Andaman’s), ship (the Victory), newspaper (the New York Times), descriptive geographical names (the Punjab), names of holy books (the Quran)* and names of noted public palaces and important events (The High Court, the Assembly House, the French Revolution, the Reformation).
b) Date of the month: the 1st June, 2003.
c) Nouns to indicate a profession: He joined the bar or the Church (i. e. became a lawyer or a clergyman).
d) A national name to denote a people collectively the expression having a plural force; “the English (=English people) are industrious. Without the, such a noun indicates the languages of the people; English= the languages of the people of England.
e) Singular is Common Noun to indicate a species or class: The dog is faithful animal.
f) A noun defined by adjective or adjectival phrases and clauses: The black dog. The man that came here yesterday.
g) A Common Noun as a substitute for the Possessive Adjective (Change of Possessive Adjective): I struck him on the (his) head. He Started me is the (my) face.
h) Singular Noun that by their very nature cannot signify more than one object: The moon, the sun, the east, the sky.
i) Adjective with plural nation to indicate a whole class of persons. But we should not combine both forms. The correct forms of sentences are:
i) The rich are not always happy.
ii) Rich men are not always happy.
iii) The rich man is not always happy.
vi) But not, the rich men are not always happy.
j) The Superlative degree: He is best of them.
k) The Comparative degree, as an adverb: The more, the merrier.
l) Some Adjectives and Nouns in the singular number to express an abstract idea: Do not leap in the dark. The future (= futurity) is unknown to us. Check the beast (=animal nature) in you.
m) An ordinal number written in letters; but when written in Roman notation, no article is used: George the fifth (but George V), Chapter the second (but Chapter II)
09. Omission of Articles-- No article is used:
a) Before Proper, Material or Abstract Nouns except when they are particularized: Ronaldo (but the kind Ronaldo), gold (but the gold of Australia).
b) Before Common Nouns in the Plural number, except when they are particularized: Dogs bark; Cows eat grass, but the dogs of my house; the cows that I brought.
c) Before Common Nouns when they are qualified by pronominal or numeral adjectives: my horse, each boy.
d) Before Common Nouns when they are used in the Vocative case: Come here, boy; Girl, don’t do it.
e) Often before, Common Nouns, preceded by the phrase a kind of species or sort of or used in its widest sense: The banyan is kind of tree. Malaria is caused by a species of mosquito. Man, bird and beast—all are subject to death.
f) Before man in the sense of mankind and before father, mother and baby when a particular one of them is meant: Man is mortal; Father or Mother (i. e. my father or mother) says so.
g) Often before nouns descriptive of rank or occupation and used in Apposition before or after Proper names: King Edward, king of England (also Edward, the King of England): Principal Bose, Principal of the college (also the Principal of the College).
But when such nouns are not used appositionally, they may or may not have articles before them: He is Premier (or the Premier) of England. He is Principal (or, the Premier) of England. He is Principal (or, the Principal) of the college. He was elected President of the meeting.
h) In many idiomatic phrases: To take foot (to be firmly established); to call to mind (to remember): to give ear (to hear), to set foot on; by boat; at night; send word; at home; to attend school; by land; on horseback, etc.
10. Names of diseases usually do not take the before them: Fever, headache, diphtheria. Sometimes however, ‘the’ may be used: the gout, the measles. “The Oxford writers “ be a martyr to gout.”