1. Characteristics of idioms

1) Semantic unity

  Each idiom is a semantic unity. The semantic unity can be reflected by the fact that the meaning of an idiom is very often not the total sum of the meanings of the constituent words. The semantic unity can also be shown in the illogical relations between the literal meanings of the constituent words and the meaning of the idiom.

2) Structural stability

  Structural stability means that the structure of an idiom usually remains unchangeable. In other words, the constituent components of an idiom can not, generally speaking, be replaced.

2. Classification of idioms

1) Idioms norminal in nature:

  They function as nouns in a sentence.

2) Idioms adjectival in nature

  They function as adjectives in a sentence.

3)Idioms verbal in nature

  They function as verbs in a sentence.

4)Idioms adverbial in nature

  They function as adverbials in a sentence.

5)Sentence idioms

  Such idioms are usually in complete sentential form. They are usually proverbs or sayings.

3.Use of idioms

1) Stylistic features                                  

  Different idioms show different stylistic meanings. Some are casual, others formal, still others neural in style. The same idiom may show stylistic differences when denoting different meanings.

2)Rhetorical features

(1)Phonetic manipulation

a. alliteration such as "chop and change"

b. rhyme such as "toil and moil"

(2)Lexical manipulation

a. reiteration, which means the duplication of synonyms such as "chop and change"

b. repetition, which means the repetition of the same word, such as "by and by"

c. juxtaposition, which means the combination of two antonyms such as "day and night"

(3) Figures of speech

a. simile: as proud as a peacock

b. metaphor: white elephant

c. metonymy: velvet glove

d. synecdoche: earn one's bread

e. personification: Failure is the mother of success      

4. Variations of idioms

1)addition: "in good condition" from "in condition"

2) deletion: "the last straw" from "It is the last straw that breaks the camel's back."

3) position-shifting: "The Johnsons keep up with sb" from "keep up with the Johnsons"

4) replacement: "wash one's clean linen in public" from "wash one's dirty linen in public"

Idioms are terse, vivid and expressive.