Morphology

"For English, [morphology] means devising ways of describing the properties of such disparate items as a, horse, took, indescribable, washing machine, and antidisestablishmentarianism. A widely recognized approach divides the field into two domains: lexical or derivational morphology studies the way in which new items of vocabulary can be built up out of combinations of elements (as in the case of in-describ-able); inflectional morphology studies the ways words vary in their form in order to express a grammatical contrast (as in the case of horses, where the ending marks plurality)."
(David Crystal, The Cambridge Encyclopedia of the English Language, 2nd ed. Cambridge Univ. Press, 2003)

The distinction between words and lexemes provides the basis for the division of morphology into two branches: inflectional morphology and lexical word-formation.

"Inflectional morphology deals with the inflectional forms of various lexemes. It has something of the character of an appendix to the syntax, the major component of the grammar. Syntax tells us when a lexeme may or must carry a certain inflectional property, while inflectional morphology tells us what form it takes when it carries that inflectional property.

"Lexical word-formation, by contrast, is related to the dictionary. It describes the processes by which new lexical bases are formed and the structure of complex lexical bases, those composed of more than one morphological element. The traditional term is simply 'word-formation.'"