Editing Posidonius (section)

==Philosophy==
For Posidonius, philosophy was the dominant master art and all the individual sciences were subordinate to philosophy, which alone could explain the cosmos. All his works, from scientific to historical, were inseparably philosophical.

He accepted the [[Stoicism|Stoic]] categorization of philosophy into physics (natural philosophy, including metaphysics and theology), logic (including dialectic), and ethics.<ref name="diog1">Diogenes Laërtius, ''The Lives and Opinions of Eminent Philosophers'', [http://www.attalus.org/old/diogenes7b.html#39 7.39–40].</ref> These three categories for him were, in Stoic fashion, inseparable and interdependent parts of an organic, natural whole. He compared them to a living being, with physics the flesh and blood, logic the bones and tendons holding the organism together, and finally ethics—the most important part—corresponding to the soul.<ref name="diog1"/><ref>Sextus Empiricus, ''Against the Professors'', 7.19.</ref>

Although a firm Stoic, Posidonius was syncretic like Panaetius and other Stoics of the middle period.<ref name="sedley22">{{Harvnb|Sedley|2003|p=22}}</ref> He followed not only the earlier Stoics, but made use of the writings of [[Plato]] and [[Aristotle]].<ref name="sedley22"/> Posidonius studied Plato's ''[[Timaeus (dialogue)|Timaeus]]'', and seems to have written a commentary on it emphasizing its [[Pythagoreanism|Pythagorean]] features.<ref name="sedley21">{{Harvnb|Sedley|2003|p=21}}</ref> As a creative philosopher, Posidonius would however be expected to create innovations within the tradition of the philosophical school to which he belonged.<ref name="sellars11">{{Harvnb|Sellars|2006|p=11}}</ref> [[David Sedley]] remarks:<ref name="sedley24"/>

{{Blockquote|On the vast majority of philosophical issues, what we know of both Panaetius and Posidonius places them firmly within the main current of Stoic debate. Their innovatively hospitable attitude to Plato and Aristotle enables them to enrich and, to a limited extent, reorientate their inherited Stoicism, but, for all that, they remain palpably Stoics, working within the established tradition.}}

===Ethics===
Ethics, Posidonius taught, is about practice not just theory.<ref name="kiddb69">{{Harvnb|Kidd|1988|p=69}}</ref> It involves knowledge of both the human and the divine, and a knowledge of the universe to which human reason is related.<ref name="kiddb69"/>

It was once the general view that Posidonius departed from the monistic psychology of the earlier Stoics.<ref name="sellars10"/> [[Chrysippus]] had written a work called ''[[On Passions]]'' in which he affirmed that reason and emotion were not separate and distinct faculties, and that [[Stoic passions|destructive passions]] were instead rational impulses which were out-of-control. According to the testimony of [[Galen]] (an adherent of Plato), Posidonius wrote his own ''On Passions'' in which he instead adopted Plato's tripartition of the soul which taught that in addition to the rational faculties, the human soul had faculties that were spirited (anger, desires for power, possessions, etc.) and desiderative (desires for sex and food).<ref name="sellars10"/> Although Galen's testimony is still accepted by some, more recent scholarship argues that Galen may have exaggerated Posidonius' views for polemical effect, and that Posidonius may have been trying to clarify and expand on Chrysippus rather than oppose him.<ref name="sellars10"/><ref name="graver216">{{Harvnb|Graver|2002|p=216}}</ref> Other writers who knew the ethical works of Posidonius, including Cicero and [[Seneca the Younger|Seneca]], grouped Chrysippus and Posidonius together and saw no opposition between them.<ref name="kiddb69"/><ref name="graver216"/>

===Physics===
The philosophical grand vision of Posidonius was that the universe itself was interconnected as an organic whole, providential and organised in all respects, from the development of the physical world to the behaviour of living creatures.<ref>{{Harvnb|Kidd|1999|pp=9–10}}</ref> Panaetius had doubted both the reality of [[divination]] and the Stoic doctrine of the future conflagration ([[ekpyrosis]]), but Posidonius wrote in favour of these ideas.<ref name="sedley24">{{Harvnb|Sedley|2003|p=24}}</ref> As a Stoic, Posidonius was an advocate of cosmic "sympathy" (συμπάθεια, ''sympatheia'')—the organic interrelation of all appearances in the world, from the sky to the Earth, as part of a rational design uniting humanity and all things in the universe. He believed valid predictions could be made from signs in nature—whether through astrology or prophetic dreams—as a kind of scientific prediction.<ref>Cicero. On Divination, i. 130; ii. 42</ref>

===Mathematics===
Posidonius was one of the first to attempt to prove [[Parallel postulate|Euclid's fifth postulate of geometry]]. He suggested changing the definition of parallel straight lines to an equivalent statement that would allow him to prove the fifth postulate. From there, Euclidean geometry could be restructured, placing the fifth postulate among the theorems instead.<ref>Trudeau, Richard. ''The Non-Euclidean Revolution'', Boston: Birkhauser, 1987, pp. 119–120.</ref>

In addition to his writings on geometry, Posidonius was credited for creating some mathematical definitions, or for articulating views on technical terms, for example 'theorem' and 'problem'.

===Astronomy and meteorology===
Some fragments of his writings on astronomy survive through the treatise by [[Cleomedes]], ''On the Circular Motions of the Celestial Bodies'', the first chapter of the second book appearing to have been mostly copied from Posidonius.

Posidonius advanced the theory that the Sun emanated a vital force that permeated the world.

He attempted to measure the distance and size of the [[Sun]]. In about 90 BC, Posidonius estimated the distance from the Earth to the Sun (see [[astronomical unit]]) to be 9,893 times the Earth's radius. This was still too small by half. In measuring the size of the Sun, however, he reached a figure larger and more accurate than those proposed by other Greek astronomers and [[Aristarchus of Samos]].<ref>Posidonius. [http://www.attalus.org/translate/poseidonius.html#215.K Fragment 215.K] from Cleomedes</ref>

Posidonius also calculated the size and distance of the [[Moon]].

Posidonius constructed an [[orrery]], possibly similar to the [[Antikythera mechanism]]. Posidonius's orrery, according to [[Cicero]], exhibited the diurnal motions of the Sun, Moon, and the five known planets.<ref>Cicero. [https://www.gutenberg.org/ebooks/14988 ''De Natura Deorum (On the Nature of the Gods)''], ii-34, p. 287.</ref>

Posidonius in his writings on meteorology followed Aristotle. He theorized on the causes of clouds, mist, wind, and rain as well as frost, hail, lightning, and rainbows. He also estimated that the boundary between the clouds and the heavens lies about 40 stadia above the Earth.

=== Geography, ethnology, and geology ===
[[File:Sphendoné,_hoc_est,_Funda_Posidonii.jpg|thumb|450px|World map according to ideas by Posidonius (150–130 BC), drawn in 1628 by cartographers [[Petrus Bertius]] and [[Melchior Tavernier]]. Many of the details could not have been known to Posidonius; rather, Bertius and Tavernier show Posidonius's ideas about the positions of the continents.]]
Posidonius's fame beyond specialized philosophical circles had begun, at the latest, in the eighties with the publication of the work "''{{visible anchor|About the ocean and the adjacent areas}}''". This work was not only an overall representation of geographical questions according to current scientific knowledge, but it served to popularize his theories about the internal connections of the world, to show how all the forces had an effect on each other and how the interconnectedness applied also to human life, to the political just as to the personal spheres.

In this work, Posidonius detailed his theory of the effect on a people's character by the climate, which included his representation of the "geography of the races". This theory was not solely scientific, but also had political implications—his Roman readers were informed that the climatic central position of Italy was an essential condition of the Roman destiny to dominate the world. As a Stoic, he did not, however, make a fundamental distinction between the civilized Romans as masters of the world and the less civilized peoples. Posidonius's writings on the Jews were probably the source of [[Diodorus Siculus]]'s account of the siege of [[Jerusalem]] and possibly also for [[Strabo]]'s.<ref>{{citation| first1= Shemuel |last1= Safrai |first2= M. |last2= Stern |title= The Jewish people in the first century: Historical Geography |page= 1124 |date= 1988 |quote=Most scholars hold that Diodorus, from Book 33 of his work onwards, depended on Posidonius}}</ref><ref>Gmirkin, Russell E. ''[[Berossus]] and Genesis, Manetho and Exodus: Hellenistic histories'', 2006, p. 54. "Jewish misanthropy was also a feature in Posidonius's account of the Jews, though in a less extreme form. 126 Diodorus Siculus, Library 40.3.4b likely derived from Posidonius, whose history may have been consulted by [[Pompey]]..."</ref><ref>Bar-Kochva, Bezalel. ''The Image of the Jews in Greek Literature: The Hellenistic Period'', 2009, p. 440. "Posidonius of apamea (d) The Anti-Jewish Libels and Accusations in Diodorus and Apion We have seen in chapters 11–12 that Posidonius used [[Moses]] and Mosaic Judaism to portray his own religious, social, and political ideals."</ref> Some of Posidonius's arguments are contested by [[Josephus]] in ''[[Against Apion]]''.

Like [[Pytheas]], Posidonius believed the [[tide]] is caused by the Moon. Posidonius was, however, wrong about the cause. Thinking that the Moon was a mixture of air and fire, he attributed the cause of the tides to the heat of the Moon, hot enough to cause the water to swell but not hot enough to evaporate it.

He recorded observations on both earthquakes and volcanoes, including accounts of the eruptions of the volcanoes in the [[Aeolian Islands]], north of [[Sicily]].

====Earth's circumference====
{{anchor|Circumference of the Earth|Calculation of Earth's circumference|Arc measurement}}
Posidonius calculated the [[Earth's circumference]] by the [[arc measurement]] method, by reference to the position of the star [[Canopus (star)|Canopus]].<ref name="Torge Müller 2012 p. 5">{{cite book | last1=Torge | first1=W. | last2=Müller | first2=J. | title=Geodesy | publisher=De Gruyter | series=De Gruyter Textbook | year=2012 | isbn=978-3110250008 | url=https://books.google.com/books?id=RcfmBQAAQBAJ&pg=PA6 | access-date=2021-05-02 | page=5}}</ref> As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at [[Alexandria]] he saw it ascend as far as 7½ degrees above the horizon (the [[meridian arc]] between the latitude of the two locales is actually 5 degrees 14 minutes). Since he thought Rhodes was 5,000 [[stadion (unit of length)|stadia]] due north of Alexandria, and the difference in the star's elevation indicated the distance between the two locales was 1/48 of the circle, he multiplied 5,000 stadia by 48 to arrive at a figure of 240,000 stadia for the circumference of the Earth.<ref name="fragment 202">Posidonius, [http://www.attalus.org/translate/poseidonius.html#202.K fragment 202]</ref>

His estimate of the latitude difference of these two points, 360 degrees/48=7.5 degrees, is rather erroneous. (The modern value is approximately 5 degrees.) In addition, they are not quite on the same meridian as they were assumed to be. The longitude difference of the points, slightly less than 2 degrees, is not negligible compared with the latitude difference.

Translating stadia into modern units of distance can be problematic, but it is generally thought that the stadion used by Posidonius was almost exactly 1/10 of a modern statute mile. Thus Posidonius's measure of 240,000 stadia translates to {{cvt|24000|mi|km}} compared to the actual circumference of {{cvt|24901|mi|km}}.<ref name="fragment 202"/>

[[File:Posidonius earth circumference.svg|thumb|250px|Posidonius's method for calculating the circumference of the Earth, relied on the [[Horizontal coordinate system|altitude]] of the star [[Canopus]]]]
Posidonius was informed in his approach to finding the Earth's circumference by [[Eratosthenes]], who a century earlier arrived at a figure of 252,000 stadia; both men's figures for the Earth's circumference were uncannily accurate.

[[Strabo]] noted that the distance between Rhodes and Alexandria is 3,750 stadia, and reported Posidonius's estimate of the Earth's circumference to be 180,000 stadia or {{cvt|18000|mi|km}}.<ref>Cleomedes ([http://adsabs.harvard.edu/abs/1975QJRAS..16..152F in Fragment 202]) stated that if the distance is measured by some other number the result will be different, and using 3,750 instead of 5,000 produces this estimation: 3,750 x 48 = 180,000; see Fischer I., (1975), ''Another Look at Eratosthenes' and Posidonius' Determinations of the Earth's Circumference'', Ql. J. of the Royal Astron. Soc., Vol. 16, p. 152.</ref> [[Pliny the Elder]] mentions Posidonius among his sources and without naming him reported his method for estimating the Earth's circumference. He noted, however, that [[Hipparchus]] had added some 26,000 stadia to Eratosthenes's estimate. The smaller value offered by Strabo and the different lengths of Greek and Roman stadia have created a persistent confusion around Posidonius's result. [[Ptolemy]] used Posidonius's lower value of 180,000 stades (about 33% too low) for the Earth's circumference in his [[Geography (Ptolemy)|''Geography'']]. This was the number used by [[Christopher Columbus]] to underestimate the distance to India as 70,000 stades.<ref>[[John Freely]], [https://books.google.com/books?id=MfhjAAAAQBAJ ''Before Galileo: The Birth of Modern Science in Medieval Europe''] (2013), {{ISBN|978-1468308501}}</ref>

===History and tactics===
In his ''Histories'', Posidonius continued the ''World History'' of [[Polybius]]. His history of the period 146–88 BC is said to have filled 52 volumes.<ref>{{Cite web|url=http://www.attalus.org/translate/poseidonius.html#T1|title=Poseidonius (Posidonius): translation of fragments|website=www.attalus.org}}</ref> His ''Histories'' continue the account of the rise and expansion of Roman dominance, which he appears to have supported. Posidonius did not follow Polybius's more detached and factual style, for Posidonius saw events as caused by human psychology; while he understood human passions and follies, he did not pardon or excuse them in his historical writing, using his narrative skill in fact to enlist the readers' approval or condemnation.

For Posidonius "history" extended beyond the earth into the sky; humanity was not isolated each in its own political history, but was a part of the cosmos. His ''Histories'' were not, therefore, concerned with isolated political history of peoples and individuals, but they included discussions of all forces and factors (geographical factors, mineral resources, climate, nutrition), which let humans act and be a part of their environment. For example, Posidonius considered the climate of Arabia and the life-giving strength of the sun, tides (taken from his book on the oceans), and climatic theory to explain people's ethnic or national characters.

Of Posidonius's work on tactics, ''The Art of War'', the Greek historian [[Arrian]] complained that it was written 'for experts', which suggests that Posidonius may have had first hand experience of military leadership or, perhaps, used knowledge he gained from his acquaintance with [[Pompey]].