If the lexical meaning of the root morpheme and the lexico-grammatical meaning of the stem coincide the word is primary,
e.g. pen - to pen, father - to father .
The nouns are names of an object and a living being. Therefore in the nouns «pen» and «father» the lexical meaning of the root and the lexico-grammatical meaning of the stem coincide.
The verbs «to pen» and « to father» denote an action, a process therefore the lexico-grammatical meanings of the stems do not coincide with the lexical meanings of the roots. The verbs have a complex semantic structure and they were converted from nouns.
2. If we compare a converted pair with a synonymic word pair which was formed by means of suffixation we can find out which of the pair is primary. This criterion can be applied only to nouns converted from verbs, e.g. «chat» n. and «chat» v. can be compared with «conversation» - «converse», «employment – employ».
3. The criterion based on derivational relations is of more universal character. In this case we must take a word-cluster of relative words to which the converted pair belongs. If the root stem of the word-cluster has suffixes added to a noun stem the noun is primary in the converted pair and vice versa, e.g. in the word-cluster : hand n., hand v., handy, handful the derived words have suffixes added to a noun stem, that is why the noun is primary and the verb is converted from it. In the word-cluster: dance n., dance v., dancer, dancing we see that the primary word is a verb and the noun is converted from it.