by Kathleen Watson (used with permission)

A reader asked me to discuss subconscious and unconscious, clarifying the implications of prefixes sub and un.

First of all, conscious means to be awake, aware, and responding to one’s surroundings.

A prefix is a letter or a group of letters that appears at the beginning of a word and changes its original meaning.

The prefixes sub and un have distinctly different meanings:

sub: under or below
substandard, subcommittee
Substandard living conditions contribute to poor health.
The subcommittee will investigate the cost of the proposal.

un: the opposite or reverse of
unlike, unwearable
She is so unlike her twin sister in temperament.
The soaked jacket was unwearable.

Your subconscious (noun) is the part of your mind just below awareness; a subconscious (adjective) thought is one of which you are not fully aware but that might influence your feelings or actions:

Trevor has a subconscious fear that his girlfriend, Jenna, will break up with him if he goes fishing this weekend.
At a subconscious level, Jenna hopes her boyfriend, Trevor, will go fishing this weekend so she can use it as an excuse to break up with him.

To be unconscious means to lose consciousness.

When Trevor fell in the fishing boat and hit his head, the jolt left him unconscious for a few seconds.
When Jenna learned that Trevor’s fall had left him temporarily unconscious, she couldn’t be mad at him for going fishing — or use it as an excuse to break up with him.

Our language is full of prefixes: anti (antidepressant), bi (bilateral), dis (disassemble), extra (extracurricular), infra (infrared), inter (interoffice), multi (multicolored), non (nonfiction), out (outperform), over (overpay), para (parasailing), post (postgraduate), pre (precondition), re (reintroduce), under (underestimate).

Note that none of these words created with a prefix requires a hyphen.

My new book Grammar for People Who Hate Rules has a list of words with these and other common prefixes, most of which don’t require a hyphen.