How can pre be used [duplicate]

Pre- (etymology)

• word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place,", Old English fore "before"), extended form of root *per- (1) "beyond" (see per).

• The Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.

Usage note:

• This prefix is usually prefixed to words without using a hyphen (for example, prefix, predate).

• A hyphen is used in the following cases:

  • Where excluding a hyphen would be likely to lead to a mispronunciation of the word because "pre" appears not to be a complete syllable (for example, "pre-yaw course", which could be read as "prey aw course" if unhyphenated).

  • Always in British English before the letter e (for example, pre-existing)

  • Often in British English before other vowels (for example, pre-operative);

  • Always in all varieties of English before a character other than a letter (for example, pre-1960).

(Wiktionary)

This is a matter of style, and as such, you should be guided by your manual of style. I use the Chicago Manual of Style, which lists pre- as a prefix that's closed (unhyphenated) when combined with other words. Exceptions are

• the word following is capitalized or starts with a numeral (pre-Enlightenment, pre-1939)

• two or more words follow (pre-Revolutionary War)

• for new coinages, when the last letter of the prefix and the first letter of the word following are the same (pre-ergotic). When these words become familiar, they also become closed (preempt).