These selectional restrictions on what base a prefix can be attached to can be used to distinguish between otherwise identical-sounding prefixes. For instance, there are two different "un-" prefixes in English: one meaning "not, opposite of", the other meaning "reverse action, deprive of, release from". The first prefix "un-" "not" is attached to adjective and participle bases while the second prefix "un-" "reverse action" is attached to either verb or noun bases. Thus, English can have two words that are pronounced and spelled the same and have the same lexical category but have different meanings, different prefixes, a different internal morphological structure, and different internal bases that the prefixes are attached to: