Morphemes (minimal units of meaning) are of two basic kinds: roots and affixes. While there is not an absolutely sharp dividing line between them, due to the natural, gradual historical progression from root to affix, there are various properties that typically cluster together, thus allowing us to distinguish the two types. For most morphemes, it is clear which class they belong in.
Affixes are subclassified by where they attach to roots. Prefixes occur before roots, suffixes are placed after a root, and infixes occur inside a root. Some languages even have circumfixes, which surround a root.
There is another type of affix called a linker or linking morpheme or filler. These don't have any function other than linking one morpheme to another within a word. The most common linker in English is -o- which occurs between roots in Latinate compund words like in petr-o-glyph.
Affixes are bound elements and roots are free. But there is another important type of free morpheme besides roots in English and these are called function words. Function words typically occur in languages like English which don't have much inflectional morphology (bound morphemes that signal grammatical categories).
Function words, like inflectional morphology, primarily serve gramnatical functions. Function words are small units that have some independence, occuring with more freedom of position than affixes (thus they are somewhat root-like), but which have grammar-like meaning rather than concrete lexical content (which makes them more affix-like). Some function words in English are the, a, he, she, it, if, although, etc.
Function words can be thought of as right in between roots and affixes. Prepositions (like English over, in, through) are sometimes classed as function words and sometimes as roots--because they are, again, intermediate. In form, they are free morphemes. In terms of function, they have (especially in their spatial meanings) more concrete lexical content than most grammatical elements, but their meaning is still rather abstract and relational. (Note that in Greek and Latin, the elements corresponding to the English prepositions are bound morphemes rather than free function words. These are the spatial prefixes such as circum-, meta-, sub-, etc.)
|ROOT > PREPOSITION > FUNCTION WORD > AFFIX|
The elements to the left are more lexical, those to the right are more grammatical.
Fortunately, we don't have to worry about the in-between cases! Probably 99% of all morphemes in English (and Latin and Greek for that matter) are easily identified by the criteria given above as either roots or affixes. Be sure you can tell the difference when looking at the morphemes in ordinary, garden-variety words.
© Suzanne Kemmer
Last modified Sept 2019