What defines base words in linguistics?

Base words in linguistics are defined as words that can have suffixes and prefixes added to them. This characteristic is fundamental to understanding how morphemes, the smallest units of meaning in a language, combine to form new words. A base word provides a root structure to which various prefixes (added to the beginning) and suffixes (added to the end) can be attached to alter its meaning or grammatical function, creating derived forms. For example, the base word "happi-" can become "happy," "happiness," or "unhappy" through the addition of various prefixes and suffixes.

This flexibility highlights the important linguistic principle that base words serve as the foundational elements from which other words are constructed, allowing for the expansion of vocabulary and expression in a language. The other options do not accurately encapsulate the defining attributes of base words in this context.