Word-groups like words may be also analysed from the point of view of their motivation. Word-groups may be called as lexically motivated if the combined lexical meaning of the group is deducible from the meaning of the components. All free phrases are completely motivated.
It follows from the above discussion that word-groups may be also classified into motivated and non-motivated units. Non-motivated word-groups are habitually described as phraseological units or idioms.
Investigations of English phraseology began not long ago. English and American linguists as a rule are busy collecting different words, word-groups and sentences which are interesting from the point of view of their origin, style, usage or some other features. All these units are habitually described as «idioms», but no attempt has been made to describe these idioms as a separate class of linguistic units or a specific class of word-groups.
In our country research in English phraseology has been constantly carried on for at least 60 years and has some results. The term «phraseological î Ñ units» to denote a specific group of phrases was introduced by Soviet linguists and is generally accepted in our country.
Great work in this field has been done by the outstanding Russian linguist A. Shakhmatov in his work «Syntax». This work was continued by Acad. V.V. Vinogradov. Great investigations of English phraseology were done by Prof. A. Cunin, I. Arnold and others.