The inflectional morphology of a language is the study of the ways in which bound grammatical morphemes combine with stems to be realised as grammatical words. On the other hand, the derivational morphology of a language is the study of the ways in which bound lexical morphemes combine with stems to be realised as lexical words.
Classical grammarians of Latin and Greek generally divided grammar into accidence, word formation and syntax. They did not pay much attention to derivation because they did not really consider it to be a part of grammar.
There are three main differences between inflection and derivation. Firstly, inflection refers to the ways in which bound grammatical words combine with stems to form grammatical words as mentioned earlier while derivation ultimately leads to the formation of lexical words. Both grammatical and lexical words ultimately surface as phonological and orthological words in which bound lexical morphemes can usually be identified as having been affixed. These affixes can be divided into inflectional and derivational affixes. Those which realise bound grammatical morphemes (such as –s, –es on plural nouns, ’s on possessive nouns and –d and –ed on the past participle forms of verbs) are called inflectional affixes and have no fixed, concrete meaning of their own while those which realise bound lexical affixes (such as –ish, –al, –able and –ness) are called derivational affixes.
Inflectional affixes never change the grammatical category of the stem: they are all suffixes which form the outer layer of complex words and modify the meaning of the steam in regular ways. This is not the case with derivational affixes which may be either suffixes or prefixes (such as de–, re– and –ize). It is possible for both inflectional and derivational morphemes to occur in the same word. The latter always constitutes the outer layer as no affix can be added after the inflectional affix has been added. Thus, derivation may have an input in...