The idioms can be classifi ed on the basis of different principles. The traditional and the oldest principle for classifi cation is based on their original content and it might be termed as thematic. On this principle they are classifi ed according to their sources of origin, referring to different spheres of human activity, life of nature, natural phenomena etc. Prof. L.P. Smith distinguishes idioms connected with the sea, agriculture, wild and domestic animals, art, etc. E.g.: in deep waters (in trouble), couch potato (about a man who spends a lot of time watching television), crocodile tears (insincere tears for effect only) etc. English idioms have many colloquial expressions with parts of human body which are called somatic phrases or it can be introduced as somatisms. E.g.: face to face (person to person), to lose one’s head (panic, lose control), under one’s nose (very close, easily noticed), easy on the eye (pleasant to look at) etc. Idioms-zoomorphisms are widely spread phraseological units where authors assign animal characteristics to human characters. E.g.: paper tiger (a person who appears to have power but is in reality ineffectual), as gentle as a lamb (very gentle person), as scared as a rabbit (very scared); a fi sh out of water (someone who is in unsuited situation), horse about/around (play or act in a wild or noisy manner) etc. There are many idioms which have key words from special categories:

 Colours – a black list (a list of persons who are considered to be dangerous), to have blue blood (be royal or aristocratic in origin);

 Numbers – a new one on me (something surprising); at sixes and sevens (in a state of confusion, muddle, disorder);

 Time – day after day (every day), rush hour (the time of day when there is a lot of traffi c), in half a minute (very soon). In modern linguistics, there is considerable confusion about the terminology associated with these word-groups. Most Russian scholars use the term “phraseological unit” which was fi rst introduced by Academician V.V. Vinogradov. There are many phraseological units and the differences between them are also a lot. That’s why it is important to say that phraseological units, or idioms, have different classifi cations based on their phraseology have been described by many authors. The most comprehensive are the doctoral theses of N.N. Amosova and A.V. Koonin. The detailed groups are given in the books on English idioms by L.P. Smith and W. Ball. The most signifi cant theories advanced for Russian Phraseology are those by V.V. Vinogradov.