Roots are the main parts of words, and there must be at least one in a word. Because of the importance of the root, there is not always a rule as to where the root will appear in a word. In the English language, there can be up to two roots in a word, but only if it is a compound word. Prefixes are a form of affixes that come at the beginning of a word.
Roots serve as the base of a word. Because there must be one root in every word, the root typically defines the meaning of the word. The groups of letters that prefixes add to words change the meaning of the root to which they are attached. Prefixes "modify or extend the meanings of words and roots," according to Long Island University.
Roots have "richer, more specific semantic content," according to Rice University. Their meanings derive from much older words, and an understanding of classical languages can greatly assist in understanding root words. Prefixes add meanings like before, after, during and inside. The meaning of the prefix can usually be linked to other prepositions.
Roots come from classical words from languages like Greek and Latin. Many root words are nearly exactly the same as the words in those languages, or at least have a similar derivation. Prefixes also come from Greek and Latin.