'A paradox uncovered by Bertrand Russell in 1901 that forced a reformulation of set theory. One version of Russell's paradox, known as barber paradox, considers a town with a male barber who, every day, shaves every man who doesn't shave himself, and no one else. Does barber shave himself ? The scenario as described requires that barber shave himself if and only if he does not ! Russell's paradox, in its original form considers set of all sets that aren't members of themselves. Most sets, it would seem, aren't members of themselves - for example, set of elephants is not an elephant - and so could be said to be "run-of-the-mill". However, some "self-swallowing" sets do contain themselves as members, such as set of all sets, or set of all things except Julius Caesar, and so on. Clearly, every set is either run-of-the-mill or self-swallowing, and no set can be both. But then, asked Russell, what about set S of all sets that aren't members of themselves ? Somehow, S is neither a member of itself nor not a member of itself.'

( See David Darling : The Universal Book of Mathematics, 2004 )

Conmathematical Resolution -

1. The Racecourse or Dichotomy Paradox -

There is no motion because that which is moved must arrive at middle of its course before it arrives at end. In order to traverse a line segment it's necessary to reach halfway point, but this requires first reaching quarter - way point, which first requires reaching eighth - way point, and so on without end. Hence motion can never begin.

This problem isn't alleviated by well - known infinite sum ½ + ¼ + 1/8 ... = 1 because Zeno is effectively insisting that sum be tackled in reverse direction. What is first term in such a series ?

( See David Darling : The Universal Book of Mathematics, 2004. )

2. Achilles and Tortoise -

This is perhaps most famous of Zeno's paradoxes.

The slower when running will never be overtaken by quicker; for that which is persuing must first reach point from which that which is fleeing started, so that slower must necessarily always be some distance ahead. Thus, Achilles, however fast he runs, will never catch plodding Tortoise who started first. And yet, of course, in real world, faster things do overtake slower ones.

3. The Arrow -

An arrow cannot move at a place at which it is not. But neither can it move at a place at which it is. But a flying arrow is always at place at which it is. That is, at any instant it is at rest. But if at no instant is it moving, then it is always at rest.

4. The Moving Blocks or Stadium -

Suppose three equal blocks, A , B, C, of width 1, with A and C moving past B at same speed in opposite directions. Then A takes one time, t, to traverse width of B, but half time, t/2, to traverse width of C. But these are same length, 1. So A takes both t and t/2 to traverse distance 1.

( See Simon Blackburn : Dictionary of Philosophy, 1996 )