Zeno of Elea
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Zeno of Elea Biography Zeno, commonly known as ‘Zeno of Elea’, was born in the 5th century B.C.E. in Elea in the Ancient Greek civilization (also known by its Roman name, Velia, and located in present day region of Campania in southern Italy). Biographical details of Zeno’s life are based primarily on Plato’s accounts in his book called Parmenides. Zeno’s birth year of 490 B.C.E. is approximated by Plato’s statement that Zeno was roughly 40 years old when Socrates was a young man [“Zeno’s Paradoxes” Stanford Encyclopedia of Philosophy]. And he died at the age of about 60 in roughly 430 B.C.E. Zeno was a disciple of Parmenides of Elea, the founder of the Eleatic school of philosophy, and Zeno is considered to be Parmenides’ most important pupil albeit Parmenides also had significant impact on Plato [Parmenides by Plato]. In terms of Zeno’s life and work, very little is reliably known. And the handful of details that have emerged are from Plato’s accounts that were based on either gossip (for example, the claim that Zeno and Parmenides were lovers [“Zeno’s Paradoxes” Stanford Encyclopedia of Philosophy]) or what modern day scholars claim to simply be fabrications of Plato for narrative purposes (for example, the story of Parmenides taking Zeno to Athens where he had encounters with Socrates [“Zeno’s Paradoxes” Internet Encyclopedia of Philosophy]). There’s another story about Zeno’s life that’s reported by Diogenes Laertius 700 years later in the 300 C.E. whereby Zeno had been arrested for supplying weapons to rebels fighting against a tyrant ruler of Elea. When caught, he wished to whisper something privately to the tyrant and is said to have bit his ear and didn’t let go until being stabbed to death [“Zeno’s Paradoxes” Internet Encyclopedia of Philosophy]. Introduction to Paradoxes A paradox is defined as a “seemingly absurd or self-contradictory statement that when investigated may prove to be well founded or false” [Oxford Dictionary]. Even though a paradox is against the common opinion, it is still a proposition that has been reached through some arguments. Therefore, in order to prove or disprove a paradoxical proposition one needs to carefully establish the validity of the arguments that lead to the absurd conclusion. Zeno can’t be regarded merely as a sophist (a philosopher who reasons with clever but fallacious arguments) because it does not appear that his aim was to simply confound by verbal trickery [Zeno’s Paradoxes by Wesley C. Salmon (page 6)]. At his time, mathematics had been brought to a high level of sophistication but one that was founded upon a series of conclusions and many believe that Zeno fervently sought to expose these conclusions. But regardless of this historical debate as to whether or not his arguments were specifically targeted against the Pythagoreans or against some other philosophical school, his arguments did compel mathematicians to distinguish arithmetic from geometry [“Zeno and the Mathematicians” by G.E.L. Owen Proceedings of the Aristotelian Society. N.S. LVIII (1957-58), 199-222]. His paradoxes are believed to have been designed to portray that attempts to provide a mathematical description of motion are quite easily entangled in contradictions [Modern Science and the Refutation of the Paradoxes of Zeno by Adolf Grunbaum]. If we take a closer look at the history of ancient greek mathematics, we notice that greek mathematicians were studying the concepts of continuity and things infinitely large or infinitely small. In particular they reached the following two hypotheses: that a finite length can be divided infinitely many times or a finite length is a composition of many small indivisible parts. There were two schools that subscribed to these hypotheses. The platonic school of thought accepted the fact that lengths can be divided infinitely many times. There was another school that accepted the second hypothesis, namely the school of Democritus rejects the theory of continuity and believed in the theory of the “atom”. However, where does Zeno and the Eleatic school lie? The answer is nowhere. The Eleatic school rejects both hypotheses, because they think that this is a fake problem. They believe that the concept of a “thing” is one that cannot be altered. The impact of his arguments exposing problems central to our understanding and our theories of space, time, continuity and infinity are illustrated by Bertrand Russell: “Zeno’s arguments, in some form, have afforded grounds for almost all [theories on these topics that] have been constructed from his time to our own” [Zeno’s Paradoxes by Wesley C. Salmon (page 5)]. Zeno’s Method Zeno’s method of argumentation and proof is also believed to be amongst the first cases of reductio ad absurdum (proof by contradiction) whereby he divided cases into separate arguments with each argument depending on some hypothesis. And his proof was based on reducing the hypothesis to absurdity [“Zeno and the Mathematicians” by G.E.L. Owen Proceedings of the Aristotelian Society. N.S. LVIII (1957-58), 199-222]. Another important characteristic of Zeno’s arguments was their ad hominem nature. His arguments assume the premises granted by his opponents and by the virtue of granting these premises, he imposes a need for his opponents to deny other (often absurd) consequences that can be deduced from the premises [The Problem of Infinity Considered Historically by Bertrand Russell]. The combination of these methods led to Zeno’s invention (or at the very least, a systematic and widespread establishment) of the dialectic method . Aristotle attributing credit to Zeno for this invention is regarded as an important reason for why Zeno has maintained an historically important position in the development of logic [Zeno’s Paradoxes by Wesley C. Salmon (page 7)]. The dialectic method necessitates a formal dialogue between two speakers and relies on an extensive use of rebuttals by reductio ad absurdum. This process was revolutionary because it embodied a shift away from poetry to a prose that required explicit premises and conclusions [“Zeno’s Paradoxes” Internet Encyclopedia of Philosophy]. Paradox 1: The Dichotomy The Dichotomy paradox is one the most interesting paradoxes proposed by Zeno. Aristotle mentions this paradox extensively in his book Physics, and he is the one that gave the name Dichotomy to the paradox. The Dichotomy paradox goes as follows: Suppose we have an object or human being named A. Also suppose we have a starting point S and an endpoint F that are different from each other, and suppose that A wants to move from S to F. Then the following happens: (1) There is an infinite sequence sequence Qp of points between S and F (namely, the point half-way from S to F, the point half-way from that point to F, the point half-way from that point to F and so on.) (2) If A moves from S to F, when it reaches F it has touched one by one in a finite time all the points in Qp . So we have the following: (a) if A moves from S to F, when it reaches F it has touched one by one all the points in a sequence of infinite points. (b) It is impossible to have touched one by one in a finite time all the points in an infinite sequence. Therefore, (3) A does not move from S to F. This is the progressive version of the paradox, there is another version that is called the regressive version, and we shall see and analyze it later. Now we shall analyze the assumptions made by Zeno and establish their validity. As we know if we want to disprove the conclusion of this argument, we need to show that at least one of the assumptions does not hold. Lets try and show that the argument “it is impossible to have touched one by one in a finite time all the points in an infinite sequence”. First, we need to define what an enumerable set is. A set (finite or infinite) is called enumerable when every element in the set can be included in a single list that has a first entry, second entry, etc. For example the set of natural numbers ℕ (an infinite set) is enumerable, with the function f(x) = x , identity function being an enumeration. We want to show that the sequence Qp is enumerable. J.A Faris in The Paradoxes of Zeno argues that this sequence is enumerable for the following reasons. Faris quotes the book Computability and Logic by Boolos and Jeffrey and assumes that there is a being that he names Zeus that has all the human and superhuman powers and it can enumerate all the elements of such a sequence in a finite time. Since Zeus has all this powers it is logical that he can “touch” all the points in the sequence Qp in a finite time. Boolos and Jeffrey provide the following argument to support the previous claim: If a set is enumerable, Zeus can enumerate it in one second by writing out an infinite list faster and faster. He spends ½ second writing the first entry in the list, ¼ second writing the second entry, ⅛ writing the third, etc. He writes each entry in half time he spent on its predecessor. At no point during the one second interval has he written out the whole list, however when one second has passed, the list is complete. [Computability and Logic, Boolos and Jeffrey]. This argument is irrefutable, simply because the being named Zeus has no reason of not being able to complete such a task.