Conscience and conscious both come from the Latin word conscius; the word elements mean “with” and “to know.” (Yes, the -science in conscience means the same thing as science itself.)
Conscience is a noun meaning “sense of the quality of one’s character and conduct,” “adherence to moral principles,” and “consideration of fairness and justice.” Confusion between conscience and conscious occurs because the latter word is sometimes used as a noun synonymous with consciousness, meaning “mental awareness,” though the longer form is usually employed.
More often, however, conscious appears as an adjective meaning “aware” or “awake,” or “involving perception or thought.” It also appears in combination with a noun in phrasal adjectives such as “budget conscious” to refer to someone who is concerned, sensitive, or vigilant about something.
and conscious can be distinguished because
the former word is qualitative — people have various
degrees of moral strength — while conscious,
as its antonym, unconscious, indicates, is
quantitative: You’re either one or the other,
whether the word is used as a noun or an adjective.