R. S. Ginzburg, S. S. Khidekel, G. Y. Knyazeva, A. A. Sankin a course in modern english

§ 23. Summary and Conclusions

1. Conversion, an exceedingly productive way of forming words in Modern English, is treated differently in linguistic literature. Some linguists define it as a morphological, others as a morphological-syntactic way of forming words, still others consider conversion from a purely syntactic angle.

2. 
   There are several criteria of semantic derivation within conversion pairs. The most universal are the semantic and the frequency criteria.
   
3. 
   On the synchronic plane conversion is regarded as a type of derivative correlation between two words making up a conversion pair.
   

4., On the diachronic plane conversion is a way of forming new words on the analogy of the semantic patterns available in the language. Diachronically distinction should be made between cases of conversion as such and those of homonymy due to the disappearance of inflections in the course of the development of the English language.

Word-Composition