1、AristotleKnowledge comes from experienceAristotlen384-322 BCEnBorn in Stagira,in Thrace,near Macedonia.nThe“Stagirite.”nSon of Nichomacus,prominent physician.nAristotle was likely trained in medicine.Platos StudentnAt age 17,Aristotle was sent to study with Plato at the Academy.nHe became Platos mos
2、t important student,remaining at the Academy 20 years,until Platos death.Aristotle becomes a royal tutor.nWhen Aristotle left the Academy in 347,he settled briefly on islands near the Ionian coast,then accepted an invitation to teach the son of the Macedonian king,Philip II,whose father had been att
3、ended by Aristotles own father.The LyceumnIn 335 BCE,Aristotle returned to Athens and established his own school,in competition with the Academy.nNamed the Lyceum,as it was adjacent to the temple to the god Apollo Lykaios.nMorning serious lecturesnEvening public lecturesnInclusive curriculumnClassif
4、ication approachnAristotle associated with AlexandernAfter Alexanders death in 323,Aristotle fled Athens to prevent“a second sin against philosophy.”Aristotles worksnWhat we have as Aristotles works are about 30 closely written,terse,treatises on a full range of philosophical and scientific topics.n
5、These may have been his morning lectures,or even students notes on those lectures.versus Platos worksnIn contrast,Platos surviving works consist of about 20 dramatic dialogues that discuss philosophical issues in a Socratic,dialectical,questioning manner.nAristotle may have written such works as wel
6、l,but they have not survived.The foundation of western philosophy and sciencenAristotles works more than Platos laid the groundwork for the systematic development of philosophy and the basic framework for the understanding of nature.nLogic,empirical evidence,systematic explanation.nSound methodology
7、,wrong conclusions.The benchmark for the understanding of naturenThe standard view of the world for 2,000 years.nTo understand the development of science it is necessary first to grasp Aristotles methods and his conclusions about nature.EmpiricismnFirst,Aristotle grounds all knowledge on experience.
8、nThis is unlike Plato for whom knowledge came only when the philosopher escaped from the world of sense perception,which could mislead.nReality,for Aristotle,was the world around us,not the objects of the mind,which could be just fantasy.Aristotle,the biologistnStudents at the Lyceum collected speci
9、mens,dissected,and classified them.nAnalysis of life forms arose from examination of many real examples.nSimilarly every subject was examined and classified.Contrasting World ViewsA basic division in how the world is understood:nPlato (pointing up)true knowledge comes from contemplating the abstract
10、 ideas.nAristotle (pointing down)true knowledge comes from close examination of the world around.Plato and Aristotle from Raphaels School of Athens.Contrasting World Views,2The ideal form,an example:nFor Plato,a geometric object,e.g.a triangle,circle,cube,etc.nThe true object exists only in the mind
11、.Actual representations are only approximate.nFor Aristotle,an animal or plant species,e.g.roses,trout,human beings,etc.nThe species is what all the instances of it have in common.LogicnThe way to knowledge beyond what is presented to the senses.nBased upon Parmenides principle of the excluded middl
12、e.nA statement is either true or false.Therefore,if it can be shown that a statement is not true,it must be false.nIf valid reasoning leads to a false conclusion,one of the premises must be false.SyllogismsnThe key component of Aristotelian logic is the syllogism.nTypical format:nMajor premise a gen
13、eral truth,or observationnMinor premise a particular fact,or specific observationnConclusion an inference implied by the two premises togetherSyllogisms,2nThe classic example of the syllogism:nMajor premise:All men are mortal.nMinor premise:Socrates is a man.nConclusion:Socrates is mortal.nIn other
14、words,what applies to all members of a group applies to each and every member.Syllogisms and LogicnAristotle worked out the forms of valid reasoning from premises.nThe principle is to combine known truths and deduce new knowledge that must be true if the premises are true.nThe method is sound.Howeve
15、rnThe conclusions from syllogistic reasoning must be true only if the premises are true.nVery often,Aristotle reasoned correctly from faulty generalizations and produced impressively argued,but nevertheless false,conclusions.nAs Plato noted,the senses can deceive.The Four CausesnA cause for Aristotl
16、e is a factor that partly determines a result.nAristotle identified four causes as the explanation for anything(or event)that is.nHow and why something came to be is understood by examining its four causes.The Four Causes,2nThe causes are:nThe Material Cause basically the stuff out of which anything
17、 is made.nThe Formal Cause the form,size,and shape of the thing.nThe Efficient Cause what put the material into the form it is in.nThe Final Cause the purpose of the thing.The Four Causes,3nAn example:The causes of a knife.nMaterial:The metal,e.g.iron,steel.nFormal:The shape of a knife sharp edge,lo
18、ng shaft,pointed end,rounded handle,etc.nEfficient:The tool maker that fashioned it.nFinal:To cut or slice.The Four Causes,4nMan-made things are easy enough to classify,but natural objects become more difficult.nWhat is the efficient cause of a tree?nWhat is the final cause of a rain shower?Or a hum
19、an being?nWhat is the material cause of a thunderclap?nThe formal cause of sunlight?The Four Causes,5nFor Aristotle,the most important cause was the final cause,that for which the thing exists.Anything is explained only by understanding its purpose.nExamples:a chair,a blackboard,a piece of chalk,a s
20、hoe.nOr,a planet,a drought,a mountain,a leopard.Aristotles logical analysis appliednFrom the logical tools developed by Aristotle,and the careful observations made and generalized,Aristotle built a complete system that explained the world as it is.nHis system shows the power of reasoning and the dan
21、gers of premature generalizations.Aristotles CosmosnClassification:There are two different parts of the world.nThere is the world all around,where things come and go;are born,live,and die;and motions start and stop.nThere is the world up in the sky,where things happen over and over again:the sun ris
22、es and sets,the seasons reoccur,the planets repeat cycles.The Sub-Lunar WorldnThe world around us includes the Earth itself,the seas,the atmosphere,and of course fire.nIt extends up to the moon,the first heavenly body.Generation and CorruptionnThe Sublunar world is the world of life.nEverything in i
23、t came into being,had a period of existence,and died.nEven motions started and stopped.nEven objects that did not appear to have a life span were subject to this process:nRocks,mountains,etc.,came into being and passed away,though over very long periods.The Material of the Sublunar WorldnAristotle a
24、ccepted the popular four elements of Empedocles as the material of the sublunar world:nEarth,Air,Fire,Water.nEverything in the sublunar world is made up of these elements,in different combinations.Natural PlacenThe elements all have a natural place in the sublunar worldnEarth and water are“heavy”and
25、 so their natural place is at the centre of the world.nFire and air are“light”and their natural place is at the outer edge of the sublunar world.nNote:“Light”does not mean“less heavy.”Natural MotionnWhen unobstructed,the elements strive to reach their natural place.This is called natural motion,and
26、requires no further explanation.nEarth is heavier than water,so it will push past water seeking the centre.nFire is lighter than air,so it pushes further outward.The Sublunar WorldForced MotionnObjects on Earth are not always in their natural place,nor do they only have natural motion.nThey may be f
27、orced to move unnaturally,by,for example,being pushed or pulled.nOr an object may be prevented from going to its natural place by being held back.Everyday Forced MotionsnA heavy object may be pulled or pushed to a new location.nWhen it is no longer being forced,it stops.nIf it is pushed off a cliff,
28、it will resume its natural motion downward,seeking its natural place.nA light object,e.g.a vessel containing air,may be pushed under waternIf released will assume its natural motion upward.The Problem with LogicnAristotles view of the world is complete and consistent.It is based on direct observatio
29、n,and logical analysis.nWhen something cannot be observed(e.g.a cause),Aristotle endeavours to discover what it must be,by reasoning from what he has already determined.Not so obvious forced motionsnThe weakness of Aristotles view of the cosmos is revealed most clearly in his analysis of forced moti
30、ons.nAristotle believed that an object would only move unnaturally,if it was pushed or pulled i.e.was in direct contact with the cause of motion.What about something thrown or shot?nConsider a rock being hurled,or an arrow shot from a bow.nThe motion of the object fits Aristotles analysis,only so lo
31、ng as it is in contact with the cause of motion the throwing arm or the bowstring.Why does the object move through the air?nAccording to Aristotle,the object resumes its natural motion(i.e.straight down)as soon as it is no longer in contact with whatever was forcing it.nBut this is obviously not so;
32、it keeps going.Aristotles Answer:nSince the world is full(no empty spaces anywhere),a rock or arrow flying through the air must be pushing the air out of the way as it flies.nThat air has to go somewhere.It goes behind the moving object and continues to push it forward.AntiperistasisnThis is the pri
33、nciple of antiperistasis “against remaining in the same place.”The weakest point in Aristotles physicsnAristotles antiperistasis argument was the most obviously contrived explanation in his physics.nIt attracted the attention of later philosophers almost immediately as a problem.The Super-Lunar Worl
34、dnThe heavens were obviously different.nMotions there repeated over and over again.nGeneration and corruption did not apply.nHeavenly objects seemed to always be there.nWhat needed explaining were the cycles.The Material of the Super-Lunar WorldnThe materials of the sublunar world have built in tend
35、encies to go to their natural places.nTherefore the material of the superlunar world must be different.The QuintessencenThere are no forced motions or contrary tendencies in the heavens,so there is only one material there.nIt is an additional and different element.nAristotle called it the“Fifth Elem
36、ent.”nIn Latin,that is the Quintessence.The Crystalline Element nThe heavens must be full(no empty space),but they look like they are empty.nSolution:The fifth element must be invisible,like glass,except for the few bits that show up,the planets and the stars.The Problem of the Planets,againnAll the
37、 natural motions of the fifth element are circular.nSince there are no forced motions,everything in the heavens must be moving in combinations of circular motions.Eudoxian SpheresnAristotle adopted the scheme of Eudoxus with spherical shells nested inside each other,all turning different ways.nBut w
38、ith a difference:nEudoxus was happy to describe the motions geometrically.nAristotle required a cause of motion.Solution:More spheresnEudoxus thought 27 spheres were enough to account for the motions of the celestial sphere and the seven planets(which include the sun and moon).But their motions were
39、 independent.nAristotle required that motion be communicated from one to another.nHe needed 55 spheres in total.The Unmoved MovernThe ultimate cause of motion in the universe is what turns the celestial sphere.nThe celestial sphere rubs up against the spheres of Saturn,which rub up against Jupiter,e
40、tc.nThat ultimate cause is the Unmoved Mover.The Aristotelian CosmosAn illustration from an edition of Aristotles On the Heavens,published in 1519.A Philosophy for 2000 YearsnAristotles scheme provided a logically consistent explanation for the motions of the heavens and life on Earth.nIt combined most of the preconceptions of his time into a grand system.nHis view remained the standard conception for nearly 2000 years.
