The main function of suffixes in Modern English is to form one part of speech from another, the secondary function is to change the lexical meaning of the same part of speech. ( e.g. «educate» is a verb, «educatee» is a noun, and « music» is a noun, «musicdom» is also a noun) .
There are different classifications of suffixes :
1. Part-of-speech classification. Suffixes which can form different parts of speech are given here :
a) noun-forming suffixes, such as : -er (criticizer), -dom (officialdom), -ism (ageism),
b) adjective-forming suffixes, such as : -able (breathable), less (symptomless), -ous (prestigious),
c) verb-forming suffixes, such Suffixation. as -ize (computerize) , -ify (micrify),
d) adverb-forming suffixes , such as : -ly (singly), -ward (tableward),
e) numeral-forming suffixes, such as -teen (sixteen), -ty (seventy).
2. Semantic classification . Suffixes changing the lexical meaning of the stem can be subdivided into groups, e.g. noun-forming suffixes can denote:
a) the agent of the action, e.g. -er (experimenter), -ist (taxist), -ent (student),
b) nationality, e.g. -ian (Russian), -ese (Japanese), -ish (English),
c) collectivity, e.g. -dom (moviedom), -ry (peasantry, -ship (readership), -ati ( literati),
d) diminutiveness, e.g. -ie (horsie), -let (booklet), -ling (gooseling), -ette (kitchenette),
e) quality, e Suffixation..g. -ness (copelessness), -ity (answerability).
3. Lexico-grammatical character of the stem. Suffixes which can be added to certain groups of stems are subdivided into:
a) suffixes added to verbal stems, such as : -er (commuter), -ing (suffering), - able (flyable), -ment (involvement), -ation (computerization),
b) suffixes added to noun stems, such as : -less (smogless), ful (roomful), -ism (adventurism), -ster (pollster), -nik (filmnik), -ish (childish),
c) suffixes added to adjective stems, such as : -en (weaken), -ly (pinkly), -ish (longish), -ness (clannishness).
4. Origin of suffixes. Here we can point out the following groups:
a) native (Germanic), such as -er,-ful, -less, -ly.
b) Romanic Suffixation., such as : -tion, -ment, -able, -eer.
c) Greek, such as : -ist, -ism, -ize.
d) Russian, such as -nik.
5. Productivity. Here we can point out the following groups:
a) productive, such as : -er, -ize, --ly, -ness.
b) semi-productive, such as : -eer, -ette, -ward.
c) non-productive , such as : -ard (drunkard), -th (length).
Suffixes can be polysemantic, such as : -er can form nouns with the following meanings : agent,doer of the action expressed by the stem (speaker), profession, occupation (teacher), a device, a tool (transmitter). While speaking about suffixes we should also mention compound suffixes which are Suffixation. added to the stem at the same time, such as -ably, -ibly, (terribly, reasonably), -ation (adaptation from adapt).
There are also disputable cases whether we have a suffix or a root morpheme in the structure of a word, in such cases we call such morphemes semi-suffixes, and words with such suffixes can be classified either as derived words or as compound words, e.g. -gate (Irangate), -burger (cheeseburger), -aholic (workaholic) etc.