According to what,does affixation fall into two subclasses: prefixation and suffixation? Explain the differences between prefixation and suffixation.
【正确答案】：According to the position which affixes occupy in words、 affixation falls into prefixation and suffixation.
Prcfixation is the formation of new words by adding prefixes to stems.Prefixes do not generally change the word-class of the stem but only modify its meaning.
Suffixation is the formation of new words by adding suffixes to stems.Unlike prefixes which primarily change the meaning of the stem,suffixes have only a small semantic role, their primary function being to change the grammatical function of stems.In other words,they mainly change the word class.
