I've often wondered why the words conscious and aware are synonyms, yet self-conscious and self-aware have such different meanings. Is there any reasoning behind this stark contrast in meaning between two compound words with such similar roots? Were their meanings always so different, or did usage cause their connotations to diverge over time?
Their roots weren't that similar:
Aware :before 1100; Middle English, variant of iwar, Old English gewær watchful (cognate with Old High German, Old Saxon giwar, German gewahr ), equivalent to ge- y- + wær ware
Conscious:1625–35; < Latin conscius sharing knowledge with, equivalent to con- con- + sci- (stem of scīre to know; see science) + -us -ous; compare nice.
Conscious was derived later, and came from Latin. Aware was derived earlier, and was derived from Old High German.
That's the reason for their difference in meaning.
The word conscious deals specifically with mental state while the word aware refers to accounting for wares - anything material or mental than one owns which might include mental facalties.