1. The subject of Lexicology and the main lexicological problems

Diachronic approach of conversion
The causes that made conversion so widely spread are to be approached diachronically. Nouns & verbs have become identical in form because of the loss of endings. When endings had disappeared, phonetic development resulted in the merging of sound forms for both elements of these pairs. The similar phenomena can be observed in words borrowed from the French language.
From the diachronic point of view distinction should be made between homonymy word pairs which appeared as a result of the loss of inflections and hose formed by conversion. The diachronic semantic analysis of the conversion pair reveals that in the course of time the semantic structure of the base may ( ) a new meaning or several meanings under the influence of the meanings of the conversion word.
Basic criteria of semantic derivation in conversion.
There are different criteria of differentiating between the source and the derived word in a conversion pair.

1. 
   The criterion of the non-correspondence between the lexical meaning of the root-morpheme and the part of speech meaning of the stem in one or the two words in a conversion pair. In the pair father – to father the noun is the name for a being.The lexical meaning of the root-morpheme corresponds to the part of speech meaning the stem. The verb to father denotes a process therefore the part of speech meaning of its stem doesn’t correspond to the lexical meaning of the root which is of a substantive character. Here the verb to father can be considered the derived member in the conversion pair.
   
2. 
   The synonymity criterion. This criterion is based on the comparison of a conversion pair with analogous synonymous word-group. E.g. comparing the conversion pair chat(v)-chat(n) with the synonymous pair of words to converse – conversation, it becomes obvious that the noun chat is the derived member as the semantic relations in the case of to chat – chat are similar to those between to converse – conversation. The synonymity criterion is considerably restricted in its application.
   
3. 
   The criterion of derivational relations. In the word cluster, for instance, hand(n)–hand(v)–handful-handy the derived words of the first degree of derivation have suffixes added to the nominal base: handful, handy. Thus, the noun hand is the center of the word cluster and the word ‘to hand’ is the derived member in the conversion pair under analysis.
   
4. 
   The criterion of semantic derivation. This criterion is based on semantic relations within conversion pairs. The existence of relations typical of denominal verbs within the conversional pair proves that the verb is derived member, the existence of relations typical of deverbal substantives marks the noun as the derived member.E.G.: the semantic relations between crowd(n) – crowd(v) - ‘an object and an action characteristic of the object’. This fact makes it possible to conclude that the verb crowd is the derived member.
   
5. 
   The criterion of the frequency of occurrence. A lower frequency value testifies to the derived character of the word in question. The noun is the derived member.
   
6. 
   The transformational criterion. The application of the transformational procedure may be illustrated by a change of a predicative syntagma into a nominal syntagma.E.G.: Roy loves nature – Roy’s love of nature. The noun love is the derived member.