The differences between lexical and inflectional morphology

Inflectional morphology, on the other hand, is concerned with the relationship within paradigms.  A paradigm, here, are the forms of the same lexeme.  These include the past, plural and possessive.  A paradigm does not change the grammatical class of its stems.  This branch of morphology deals with “semantic opposition among categories” and the formal means, such as inflections, that enable the discrimination between morphosyntactic categories.  A morphosyntactic category is one in which criteria from morphology and syntax apply.

To give you a specific example of the differences between inflectional and lexical, nations and nation are both parts of the same paradigm, national and nation, however, are different lexemes.  However, to say that the two morphologies can be differentiated because they are different parts of speech is incorrect.  In addition, to say that the separate entries in dictionaries are lexemes and that within each entry are to be found the parts of the paradigm is not necessarily true.  For one thing, dictionaries are not written for this purpose, and second, morphology is not based on the dictionary.  Additionally, words can have separate entries in the dictionary and still be syntactically similar.

In its simplest form then, the difference between lexical morphology and inflectional morphology is that the former deals with words of differing meaning but with a similar phonology, while the latter deals with words of the same meaning, but in different tenses.