Semantic Feature of Idioms

According  to  the  semantic  feature,  the  ready-made  phraseological  units,  idioms,  have  nearly  nothing  to  do with  their  separate  components;  the  meaning  of  such  a  unit  is  entirely  new,  and  the  current  meanings  of  the  constituents far removed . Such an example is:
 

To say black is white

This idiom means ‘to lie’. It has absolutely  nothing  in  common  with  its  constituents  and  if  we  try  to  understand  its  meaning  according  to  them,  we   shall  misunderstand  it.                             
Academician  Vinogradov  described  the  semantic  change  as  a  meaning  which  results  from  a  peculiar  chemical  combination  of  words. (Arnold I. V.)              

This  seems a really nice  comparison  because  an  entirely  new  quality  comes  into  existence. The  semantic  shift  affecting  phraseological  units  does not  consist  in  a  mere  change  of  meanings  of  each  separate  constituent  part  of  the  unit. The  meanings  of  the  constituents  merge  to  produce  an  entirely  new  meaning. Another example is:

Idioms Vs. Free Word-Groups

Word-groups  are  structurally  complex  units  consisting  of  formally  separable  elements,  which  are  functionally  equivalent  to  separate  words (Alexandrova, Ter Minasova). As  complex  units,  word-groups  or  word  combinations  are  characterized  by  a  certain  degree  of  globality  of  nomination. 

This  means  that  we  do  not  merely  bring  separate  words  together  in  a  linear  sequence,  but  we  use prefabricated  blocks  that  exist  in  a  language  as  ready-made  units  and correspondingly  function  in  speech  as  single  units. A  lot  of  theoretical  aspects  are  included  in  the  discussion  of  word-groups,  which  can  be  grouped  around  two  main  notions.

Features of English Idioms

Phraseological units or idioms are characterized by a double sense: the current meanings of constituent words build up a certain picture, but the actual meaning of the whole unit has little or nothing to do with that picture in itself creating an entirely new image. Such examples are:

To paint the town red

If we take the constituent words separately we'll see that this idiom's meaning is, ‘To paint all the buildings of the town red’. But as a whole it means, ‘To go out and party; have a good time.’

Grass is always greener on the other side.
This idiom does not mean grass which one side is green and the other one has lost its colour. Its entire meaning is 'a place or situation that is far away or different seems better than one's present situation'. Thus, these ready-made constructions display semantic integrity; functional, semantic, and lexical stability. We can’t replace the members of the word groups at our will or change them without having to the overall meaning.

Phraseology: What are Idioms?

It is  not  accidental  that  Phraseology  is  a  branch  of  Linguistics  because  it  is  a  self  sustained  discipline  with  its  object  of  investigation,  methods  of  analyses  and  perspective  of  development. 

The  term  ''phraseology''   is  a  stylistic  one  meaning  mode  of  expression,  peculiarities  of  diction, i.e choice  and arrangement  of  words  and  phrases  characteristic  of  some  author  or  some  literary  work. Phraseology  has  gained  importance  throughout  the  world. As  to  the  English  language,  the  number  of  works  devoted  to  Phraseology  is so great  that  it  is  impossible  to  enumerate  them. That  Phraseology  is  an  extensive  field  of  investigation  can  be  explained  by  two  interrelated  factors.