The modern aesthetic tries to be a bit critical about when to hyphenate, so that there are not superfluous hyphens eating up real estate on our pages, nor stopping the eye in its course of reading. For the same reason that Write and Polish eschews the serial or "Oxford" comma as unnecessary, we appreciate this style trend.
What it means, however, is that not every case is the same. Generally, attach prefixes (and suffixes) to their respective roots, as in nonprofit, semiconscious and multinational.
Exceptions — use a hyphen when:
- the prefix comes before a proper (capitalized) noun or a numeral: un-American, sub-Saharan, mid-1850s
- the closed (attached) form would double i's or a's: anti-intellectual, ultra-acidic
- the words are de-emphasize or co-owner
- using self-, other than for selfless and selfish: self-assured, self-respect, self-addressed
- using ex-: ex-wife, ex-soldier
- using re- to mean "again" AND closing the word would create confusion: I must re-cover this chair; We hope that he will recover from his injury; The proposal will be reissued; The tablecloth needs to be re-pressed*
This set of exceptions is not exhaustive, but considers many of the cases that the average person will encounter. If a specific situation with which you've struggled is not addressed here, you may need to consult a dictionary or a style manual appropriate to your business or pursuit.
You may also always contact us for clarification or to research a specific language challenge!
* As it fell out, yesterday's query turned on that we were instructing someone to "retell a story." So, no hyphen!