The Greek word a-poria can be separated into its two morphemes a- and poros (“without” and “passage”). Poros has a wide range of meanings, including way out and expedient. Some would say that Greek philosophy evolved from the problem of aporia, understood as a discursive technique to point out those questions, which mankind is unable to resolve.
“Aporia”, writes Aristotle, “is an equality between contrary reasonings [that] would seem to be a cause of perplexity; for it is when we reflect on both sides of a question and find everything alike to be in keeping with either course that we are perplexed which of the two we are to do.” (Aristotle, Topics, in Complete Works, ed. Jonathan Barnes, 2 vols. Princeton: Princeton University Press, 1984; Book 8, I:245, 145b)