in any case aristotle found it expedient to set out upon a journey that carried him to various parts of the greek world, particularly to asia minor.  while there he married and engaged in the study of biology and natural history, always his chief love.

in 342 b.c. he was called to macedon.  the son of amyntas ii had succeeded to the throne of macedon as philip ii while aristotle was at the academy, and now the king wanted the son of his father's physician back at court.  the purpose was to install him as tutor for his fourteen-year-old son, alexander the great. 

aristotle held this position for several years.  since alexander was to become alexander the great, the conqueror of persia, we have the spectacle of the greatest soldier of ancient times being tutored by the greatest thinker.

in 336 b.c. philip ii was assassinated and his son succeeded as alexander iii.  alexander had no further time for education so aristotle left macedon the next year and went back to athens while alexander went on to invade the persian empire in a great conquering campaign.  aristotle's nephew, callisthenes, accompanied alexander, but aristotle's influence over his erstwhile pupil was not very great for in 327 b.c. callisthenes was executed by the increasingly megalomaniac monarch.

meanwhile, in athens, aristotle founded a school of his own, the lyceum, so called because aristotle lectured in a hall near the temple to apollo lykaios (apollo, the wolf-god).  it was also called the "peripatetic school" (walk about) because aristotle, at least on occasion, lectured to students while walking in the school's garden.  he also built up a collection of manuscripts a very early example of a "university library."  it was this which eventually served as the kernel for the great library at alexandria.

the school continued under aristotle's directorship quite successfully, emphasizing natural philosophy.  in 323 b.c., however, the news arrived of the death of alexander the great in babylon. since aristotle was well known to have been alexander's tutor, he feared that an anti macedonian reaction in athens might lead to trouble.  and, indeed, the accusation of "impiety" was raised.  aristotle had no mind to suffer the fate of socrates.  saying he would not allow athens to "sin twice against philosophy" he prudently retired to chalcis, his mother's hometown, and died there the next year.

 aristotle's lectures were collected into nearly 150 volumes and represent almost a one-man encyclopedia of the knowledge of the times, much of it representing the original thought and observation of aristotle himself.  nor was it confined entirely to science, for aristotle dealt with politics, literary criticism, and ethics.  altogether, of the volumes attributed to him, some fifty have survived (not all of which are certainly authentic), a survival record second only to that of plato.  this survival came about through a fortunate chance. many of his manuscripts were found in a pit in asia minor about 80 b.c. by men in the army of the roman general sulla.  they were then brought to rome and recopied.

the one field for which aristotle is not noted is mathematics, but even here he may be credited with a glancing blow, for he is the virtual founder of the systematic study of logic, which is allied to mathematics.  he developed, in great and satisfying detail, the art of reasoning from statement to necessary conclusion and thereby demonstrating the validity of a line of thought.  his system stood without major change until the nineteenth-century development of symbolic logic by boole, which converted logic in to a branch of mathematics in form as well as spirit.

aristotle's most successful scientific writings were those on biology.  he was a careful and meticulous observer who fascinated by the task of classifying animal species and arranging them into hierarchies.  he dealt with over five hundred animal species in this way and dissected nearly fifty of them.  his mode of classification was reasonable and, in some cases, strikingly modern.  he was particularly interested in sea life and observed that the dolphin brought forth its young alive and nourished the fetus by means of a special organ called a placenta. no fish did this, but all mammals did, so aristotle classed the dolphin with the beasts of the field rather than with the fish of the sea.  his successors did not follow his lead, however, and it took two thousand years for biologists to catch up to aristotle in this respect.

it was j. muller who finally confirmed aristotle in this respect.  aristotle also studied viviparous sharks, those that bear live young -- but without a mammalian placenta.  he also noted the odd ability of the torpedo fish to stun its prey though, of course, he knew nothing of the electric shock with which it managed it.  he was also wrong on occasion, as when he denied sexuality in plants.  nineteen centuries were to pass before alpini was to correct this particular error.

his formation of a hierarchy of living things led him irresistibly toward the idea that animals represented a chain of progressive change, a sort of evolution.  other greek philosophers groped similarly in this direction. however, barring any knowledge as to the physical mechanism whereby evolutionary changes could be brought about, such theories invariably became mystical.  a rational theory of evolution had to await darwin, 2200 years after the time of aristotle.

aristotle studied the developing embryo of the chick and the complex stomach of cattle.  he decided that no animal had both tusks and horns, and that no single hoofed animal had horns.  but his intuition sometimes led him astray.  he believed the heart was the center of life and considered the brain merely a cooling organ for the blood.

in physics aristotle was far less successful than in biology, perhaps because he was too platonic. he accepted the heavenly spheres of eudoxus and callippus and even added further to them, reaching a total of 54. he seemed to think of the spheres as having an actual physical existence whereas eudoxus probably thought of them as imaginary aids to calculation, as we consider the lines of latitude and longitude we draw on a map. aristotle also accepted the four elements of empedocles but restricted them to earth itself. he suggested a fifth element "aether," of which all the heavens were composed. (we still use phrases such as "ethereal heights" today.)

this line of reasoning led him to agree with the pythagoreans that earth and heaven were subjected to two different sets of natural law.  on earth all things were changeable and corrupt, while in the heavens all was permanent and unchanging.  on earth the four elements each had its own place, and motion was an attempt to reach that place.  earth was in the center, water above it, air above that, and fire highest of all the earthly substances.  therefore an object composed largely of earth, such as a rock, would, if suspended in air, fall downward, while bubbles of air trapped under water would move upward.  again rain fell, but fire rose.

it also seemed to aristotle that the heavier an object was, the more eagerly it would strive to achieve its proper place since the heaviness was the manifestation of its eagerness to return.  hence a heavier object would fall more rapidly than a lighter one.  nineteen centuries later, a reconsideration of this problem by galileo was to lead to momentous consequences.  the motion of heavenly objects, on the other hand, was no attempt to get anywhere.  it was a steady, permanent motion, even and circular.

aristotle, apparently, was not an experimentalist for all that he was a close observer.  he observed that rocks fell more quickly than feathers, but he made no attempt to arrange an observation of the falling of rocks of graded weight.  furthermore, neither he nor any other ancient scholar properly appreciated the importance of precise, quantitative measurement.  this was not mere perversity on their part, for the state of instrumentation was rudimentary indeed in ancient times and there were few clear methods of making accurate measurements. in particular, they could not measure small intervals of time accurately, a deficiency that was to remain for two thousand years until the time of huygens.

aristotle rejected democritus' atomism, dooming that concept through ancient and medieval times. on the other hand, he accepted the pythagorean notion of the roundness of earth, presenting his reasoning in a fashion that remains valid today. the most telling argument was that as one travels north, new stars appear at the northern horizon while old ones disappear at the southern. if earth were flat, all stars would be equally visible from all points on its surface. it was aristotle's championing of this view that kept it alive through the darkest days that were to follow.

aristotle's system of philosophy was never as influential in ancient times as plato's. indeed, aristotle's works may not have been published for some centuries after his death. after the fall of rome, his work was largely lost to europe (only organon, his work on logic, was saved) while plato's works were, for the most part, retained. however, aristotle's books survived among the arabs, who valued them highly.

christian europe regained aristotle from the arabs, translating his books into latin in the twelfth and thirteenth centuries.  from that time aristotle replaced plato as the philosopher.  his views came to be regarded as possessing an almost divine authority, so that if aristotle said it was so, it was so. by a queer fatality, it almost seemed as though his statements were most accepted when they were most incorrect.

this cannot be blamed on aristotle, who was himself no believer in blind obedience to authority. nevertheless, following the era of over-adulation, he became the very symbol of wrongness, and when the scientific revolution took place in the sixteenth and seventeenth centuries, its first victories involved the overthrow of aristotelian physics. in the centuries since, aristotle has, as a consequence, too often been viewed as an enemy of science, whereas actually he was one of the truly great scientists of all time and even his wrongness was rational. no man should be blamed for the stubborn orthodoxy of those who many centuries later insist they speak in his name.

aristotle's teachings

as greek intellectual development after plato continued through its phases, its formers, with great unanimity, adhered to organicism.  aristotle is very typical.  a resolute critic of plato's main philosophical construct, the theory of ideas, aristotle remained nonetheless faithful to the basic tenet of the socratic program: nature was to be understood as something like man himself -- moving toward goals, striving toward the best possible arrangement, in short, acting like an organism.  he was convinced that the universe was supremely a living being both in its entirety and in its parts.

in fact, it is in aristotle's physics that one finds the first simultaneous occurrence of the terms microcosmos and megacosmos (macrocosmos), terms which were to serve as the characteristic stamp on every organismic theory about the universe until the very modern times. in the eighth book of the physics, aristotle reviewed several objections to a fundamental doctrine of his, the eternity of motion.  according to these objections, motion need not always be caused by another motion but could at times be preceded by absolute rest.  for proof, one of the arguments refers to the case of living beings, to human consciousness and animal behavior in particular.

...the animal...we say, moves itself; therefore, if an animal is ever in a state of rest, we have thing in which motion can be produced from the thing itself, and not from without. we see nothing like this in the case of inaminate things, which are always set in motion by something else from without: the animal, on the other hand, we say, moves itself; therefore, if an animal es ever in a state of abosolute rest, we have a motionless thing in which motion can be produced from the thing itself, and not from without. now if this can occur in an animal, why should not the same be true also of the universe as a whole? if it can occur in a small world [microcosmos] it could also occur in a great one [megacosmos]...

when faced with objections based manifestly on principles diametrically opposite to his own, aristotle's phrases betrayed hardly any hesitancy or surprise. thus in a highly revealing passage of the second book of the physics aristotle drew a sharp contrast between the early physics and what physics really ought to be. according to the former, nature does not work for the sake of something or because it is better one way than another; it rather works of necessity, that is, in a regularly repeated pattern of sequences. the necessity and regularity of his predecessors' physics had, however, been dependent on chance, and aristotle eagerly seized on this obvious inconsistency. chance, aristotle argued, does not repeat things in a regular fashion. regularity can be assigned only to purposeful action, which, as he contended, always works for an end and originates from the particular nature that is acting. it was at this point that aristotle reaffirmed the basic goal of socrates' arguments: the restoration of unity between man and nature in an organic whole. the declaration of a perfect parallelism between the way man acts and the manner in which nature operates could not be more explicit:

as in human operations, so in natural processes; and as in processes, so in human operations (unless someting interferes). human operations are for an end, hence natural processes are so too.". .

for it is not enough to say what are the stuffs out of which an animal is formed, to state, for instance, that it is made of fire or earth -- if we were discussing a couch or the like, we should try to determine its form rather than its matter (e.g. bronze or wood), or if not, we should give the matter of the whole. ... for the formal nature is of greater importance than the material nature...

for the formal nature is of greater importance than the material nature...

...the true object of architecture is not bricks, mortar, or timber, but the house; and so the principal object of natural philosophy is not the material elements, but their composition, and the totality of the substance, independently of which they have no existence...

in general, our quarrel with those who speak of movements in this way cannot be confined to the parts; it concerns the whole universe...

all the things mentioned [things that exist by nature] plainly differ from things which are not constituted by nature. for each of them has within itself a principle of motion and of stationariness (in respect place, or of growth and decrease, or by way of alteration).7

all natural bodies and magnitudes we hold to be, as such, capable of locomotion; for nature, we say, is their principle of movement.8

...whenever there is plainly some final end, to which a motion tends should nothing stand in the way, we always say that the one is for the sake of the other...

was natural, careful consideration will show that there was already a world.

this statement, directed against the notion of atoms whirling in space in every direction before the present configuration of things came to take shape, should forcefully intimate the multitude and sweep of conclusions that aristotle derived from the concept of natural motion. after all, his universe was a "huge nature" of which all parts were moving, striving, and yearning toward their respective ends.