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{{Short description|Virtue-focused philosophical system}}
{{Use dmy dates|date=May 2018}}

[[File:Paolo Monti - Servizio fotografico (Napoli, 1969) - BEIC 6353768.jpg|thumb|A bust of [[Zeno of Citium]], considered the founder of Stoicism]]

'''Stoicism''' is a [[Hellenistic philosophy]] that flourished in [[ancient Greece]] and [[ancient Rome|Rome]].<ref>{{cite web|title=Stoicism|website=Britannica|author=Jason Lewis Saunders|url=https://www.britannica.com/topic/Stoicism|access-date=2 January 2022|archive-date=28 June 2023|archive-url=https://web.archive.org/web/20230628193627/https://www.britannica.com/topic/Stoicism|url-status=live}}</ref> The Stoics believed that the universe operated according to reason, ''i.e.'' by a God which is immersed in nature itself.<ref name="shenefeltwhite74">{{Harvnb|Shenefelt|White|2013|p=74}}</ref> Of all the schools of ancient philosophy, Stoicism made the greatest claim to being utterly systematic.{{sfn|Long|Sedley|1987|p=160}} 

The Stoics  provided a unified account of the world, constructed from ideals of [[logic]], [[monism|monistic]] physics, and [[Naturalism (philosophy)|naturalistic]] ethics.<ref>Aetius, Stoicorum Veterum Fragmenta, 2.35</ref> These three ideals constitute virtue, which is necessary for 'living a well-reasoned life', seeing as they are all parts of a [[Logos|''logos'']], or philosophical discourse, which includes the mind's rational dialogue with itself.{{sfn|Long|Sedley|1987|p=161}} Its logic focuses on reasoning through [[Proposition|propositions]], [[Argument|arguments]], and the differentiation between truth and falsehood. Its ethics centers on virtue as the highest good, cultivating emotional [[self-control]] and rational judgment to attain ''[[eudaimonia]]'', while viewing passions as misguided judgments to be mastered. 

Stoicism was founded in the [[ancient Agora of Athens]] by [[Zeno of Citium]] around 300 BCE, and flourished throughout the [[Greco-Roman world]] until the 3rd century CE. Stoicism emerged from the [[Cynicism (philosophy)|Cynic]] tradition and was popularized through public teaching at the [[Stoa Poikile]], a painted [[colonnade]]. Among its adherents was Roman Emperor [[Marcus Aurelius]]. 

Along with Aristotelian [[term logic]], the system of [[propositional logic]] developed by the Stoics was one of the two great systems of logic in the classical world. It was largely built and shaped by [[Chrysippus]], the third head of the Stoic school in the 3rd century&nbsp;BCE. Chrysippus's logic differed from [[term logic]] because it was based on the analysis of [[proposition]]s rather than terms. Stoicism experienced a decline after [[Christianity]] became the state religion in the 4th century CE, although [[Neoplatonism and Gnosticism|Gnosticism]] lingered and incorporated pure elements of Stoicism and [[Platonism|Platoism]].

Since then, it has seen revivals, notably in the [[Renaissance philosophy|Renaissance]] ([[Neostoicism]]) and in the contemporary era.<ref>{{cite book|last1=Becker|first1=Lawrence C.|author-link=Lawrence C. Becker|title=A New Stoicism|date=2001|publisher=[[Princeton University Press]]|location=Princeton|isbn=978-1400822447|url=https://books.google.com/books?id=NbqFt3RPsuQC|access-date=10 August 2017|archive-date=8 July 2023|archive-url=https://web.archive.org/web/20230708093213/https://books.google.com/books?id=NbqFt3RPsuQC|url-status=live}}</ref> Its influence extended to Roman thinkers like [[Seneca the Younger|Seneca]] and [[Epictetus]] and later influenced Christianity and the Renaissance Neostoicism movement. Stoicism shaped subsequent developments in logic and inspired modern [[Cognitive therapy|cognitive therapies]]. 

==History==
{{seealso|List of Stoic philosophers}}
The name ''Stoicism'' derives from the ''[[Stoa Poikile]]'' ([[Ancient Greek]]: ἡ ποικίλη στοά), or "painted porch", a [[colonnade]] decorated with mythic and historical battle scenes on the north side of the [[Ancient Agora of Athens|Agora]] in [[Athens]] where [[Zeno of Citium]] and his followers gathered to discuss their ideas, near the end of the fourth century BCE.<ref>{{cite book | last = Becker | first = Lawrence | title = A History of Western Ethics | publisher = Routledge | location = New York | year = 2003 | isbn = 978-0415968256 |page=27}}</ref> Unlike the [[Epicureans]], Zeno chose to teach his philosophy in a public space. Stoicism was originally known as Zenonism. However, this name was soon dropped, probably because the Stoics did not consider their founders to be perfectly wise and to avoid the risk of the philosophy becoming a [[cult of personality]].<ref name=":1">{{Cite book|title=Stoicism and the Art of Happiness|last=Robertson|first=Donald|publisher=[[John Murray (publishing house)|John Murray]]| year= 2018| location=Great Britain}}</ref>

Zeno's ideas developed from those of the [[Cynicism (philosophy)|Cynics]] (brought to him by [[Crates of Thebes]]), whose founding father, [[Antisthenes]], had been a disciple of [[Socrates]]. Zeno's most influential successor was [[Chrysippus]], who followed [[Cleanthes]] as leader of the school, and was responsible for molding what is now called Stoicism.<ref>{{cite web |title=Chrysippus {{!}} Internet Encyclopedia of Philosophy |url=https://iep.utm.edu/chrysippus/ |access-date=31 August 2023 |archive-date=9 October 2023 |archive-url=https://web.archive.org/web/20231009152625/https://iep.utm.edu/chrysippus/ |url-status=live }}</ref> Stoicism became the foremost popular philosophy among the educated elite in the Hellenistic world and the Roman Empire<ref>{{cite book|title=These Were the Greeks|last=Amos|first=H.|publisher=Dufour Editions|year=1982|isbn=978-0802312754|location=Chester Springs|oclc=9048254}}</ref> to the point where, in the words of [[Gilbert Murray]], "nearly all the [[diadochi|successors of Alexander]] [...] professed themselves Stoics".<ref>Gilbert Murray, ''The Stoic Philosophy'' (1915), p. 25. In Bertrand Russell, ''A History of Western Philosophy'' (1946).</ref> Later Roman Stoics focused on promoting a life in harmony within the universe, within which we are active participants.

Scholars<ref>Sedley, D. (2003) The School, from Zeno to Arius Didymus. In: B. Inwood (ed.) The Cambridge Companion to the Stoics. Cambridge University Press.</ref> usually divide the history of Stoicism into three phases: the Early Stoa, from Zeno's founding to [[Antipater of Tarsus|Antipater]]; the Middle Stoa, including [[Panaetius]] and [[Posidonius]]; and the Late Stoa, including [[Gaius Musonius Rufus|Musonius Rufus]], [[Seneca the Younger|Seneca]], [[Epictetus]], and [[Marcus Aurelius]]. No complete works survived from the first two phases of Stoicism. Only Roman texts from the Late Stoa survived.<ref>A.A.Long, ''Hellenistic Philosophy'', p. 115.</ref>

==Logic==
{{See also|History of logic}}
[[File:Detail. Marble bust of Chrysippus. Roman copy (1st century CE) of an original (c. 200 BCE). Altes Museum, Berlin, Germany.jpg|thumb|[[Chrysippus]], the third leader of the Stoic school, wrote more than 300 books on logic. His works were lost, but an outline of his logical system may be reconstructed from fragments and testimony.]]
{{anchor|logic}}

For the Stoics, logic (''logike'') was the part of philosophy which examined reason (''logos'').<ref name="sellars55">{{Harvnb|Sellars|2006|p=55}}</ref> To achieve a happy life—a life worth living—requires logical thought.<ref name="shenefeltwhite74"/> The Stoics held that an understanding of ethics was impossible without logic.<ref name="shenefeltwhite78">{{Harvnb|Shenefelt|White|2013|p=78}}</ref>  In the words of Inwood, the Stoics believed that:<ref>{{Harvnb|Inwood|2003|p=229}}</ref>
{{blockquote|Logic helps a person see what is the case, reason effectively about practical affairs, stand his or her ground amid confusion, differentiate the certain from the probable, and so forth.}}

To the Stoics, logic was a wide field of knowledge which included the study of [[philosophy of language|language]], [[grammar]], [[rhetoric]] and [[epistemology]].<ref name="sellars55"/> However, all of these fields were interrelated, and the Stoics developed their logic (or "dialectic") within the context of their theory of language and epistemology.<ref name="otoolejennings400">{{Harvnb|O'Toole|Jennings|2004|p=400}}</ref> 

The Stoic tradition of logic originated in the 4th-century BCE in a different school of philosophy known as the [[Megarian school]].<ref name="bobzien880">{{Harvnb|Bobzien|1996a|p=880}}</ref> It was two dialecticians of this school, [[Diodorus Cronus]] and his pupil [[Philo the Dialectician|Philo]], who developed their own theories of [[Modal logic|modalities]] and of [[Material conditional|conditional propositions]].<ref name="bobzien880"/> The founder of Stoicism, Zeno of Citium, studied under the Megarians, and he was said to have been a fellow pupil with Philo.<ref name="sellars56">{{Harvnb|Sellars|2006|p=56}}</ref> 

However, the outstanding figure in the development of Stoic logic was [[Chrysippus|Chrysippus of Soli]] (c. 279 – c. 206 BCE), the third head of the Stoic school.<ref name="bobzien880"/> Chrysippus shaped much of Stoic logic as we know it, creating a system of propositional logic.<ref name="shenefeltwhite80">{{Harvnb|Shenefelt|White|2013|p=80}}</ref> The logical writings by Chrysippus are, however, almost entirely lost,<ref name="bobzien880"/> instead his system has to be reconstructed from the partial and incomplete accounts preserved in the works of later authors.<ref name="sellars56"/>

=== Assertibles ===
The smallest unit in Stoic logic is an ''assertible'' ({{transliteration|grc|axiomata}}), a proposition which is either true or false and which either affirms or denies.<ref name="sellars58">{{Harvnb|Sellars|2006|p=58}}</ref> Examples of assertibles include "it is night", "it is raining this afternoon", and "no one is walking."<ref name="sellars58-9">{{Harvnb|Sellars|2006|pp=58–59}}</ref><ref name="bobzien102">{{Harvnb|Bobzien|1999|p=102}}</ref> Assertibles have a truth-value such that they are only true or false depending on when it was expressed (e.g. the assertible "it is night" will only be true if it is true that it is night).{{sfn|Bobzien|1999|pp=95}} The Stoics catalogued these simple assertibles according to whether they are affirmative or negative, and whether they are definite or indefinite (or both).<ref name="bobzien97-8">{{Harvnb|Bobzien|1999|pp=97–98}}</ref> 

====Compound assertibles ====
{| class="wikitable floatright"
! colspan="3" style="background:white;text-align:center;" |
Logical connectives
|-
! Name
! Example
|-
|style="white-space:nowrap;" | [[Material conditional|Conditional]]
|style="white-space:nowrap;" | '''if''' it is day, it is light
|-
|style="white-space:nowrap;" | [[Logical conjunction|Conjunction]]
|style="white-space:nowrap;" | it is day '''and''' light
|-
|style="white-space:nowrap;" | [[Logical disjunction|Disjunction]]
|style="white-space:nowrap;" | '''either''' it is day '''or''' night
|-
|style="white-space:nowrap;" | Pseudo-conditional
|style="white-space:nowrap;" | '''since''' it is day, it is light
|-
|style="white-space:nowrap;" | [[Causality|Causal]]
|style="white-space:nowrap;" | '''because''' it is day, it is light
|-
|style="white-space:nowrap;" | Comparative
|style="white-space:nowrap;" | '''more likely''' it is day '''than''' night
|}
Compound assertibles can be built up from simple ones through the use of [[logical connectives]], which examine choice and consequence such as "if ... then", "either ... or", and "not both".<ref name="shenefeltwhite78"/><ref name="shenefeltwhite79">{{Harvnb|Shenefelt|White|2013|p=79}}</ref> Chrysippus seems to have been responsible for introducing the three main types of connectives: the [[Material conditional|conditional]] ('''if'''), [[Logical conjunction|conjunctive]] ('''and'''), and [[Logical disjunction|disjunctive]] ('''or''').<ref name="bobzien105">{{Harvnb|Bobzien|1999|p=105}}</ref> A typical conditional takes the form of "if p then q";<ref name="bobzien106">{{Harvnb|Bobzien|1999|p=106}}</ref> whereas a conjunction takes the form of "both p and q";<ref name="bobzien106"/> and a disjunction takes the form of "either p or q".<ref name="bobzien109">{{Harvnb|Bobzien|1999|p=109}}</ref> The '''or''' they used is [[Exclusive or|exclusive]], unlike the [[Logical disjunction|inclusive or]] generally used in modern formal logic.<ref>{{Harvnb|Inwood|2003|p=231}}</ref> These connectives are combined with the use of '''not''' for negation.<ref name="sellars60">{{Harvnb|Sellars|2006|p=60}}</ref> Thus the conditional can take the following four forms:<ref name="bobzien129">{{Harvnb|Bobzien|1999|p=129}}</ref> 1) "If p, then q" 2) "If not p, then q" 3) "If p, then not q" 4) "If not p, then not q." Later Stoics added more connectives: the pseudo-conditional took the form of "since p then q"; and the causal assertible took the form of "because p then q".{{Ref label|A|a|none}} There was also a comparative (or dissertive): "more/less (likely) p than q".<ref name="bobzien109-111">{{Harvnb|Bobzien|1999|pp=109–111}}</ref>

==== Modal assertibles ====
Assertibles can also be distinguished by their [[Modal logic|modal properties]]{{Ref label|B|b|none}}—whether they are possible, impossible, necessary, or non-necessary.<ref name="sellars59">{{Harvnb|Sellars|2006|p=59}}</ref> In this, the Stoics were building on an earlier Megarian debate initiated by Diodorus Cronus.<ref name="sellars59"/> Diodorus had defined ''possibility'' in a way which seemed to adopt a form of [[fatalism]].<ref name="kenny136">{{Harvnb|Adamson|2015|p=136}}</ref> Diodorus defined ''possible'' as "that which either is or will be true".<ref name="ancientlogic">{{harvnb|Bobzien|2020}}</ref> Thus, there are no forever unrealised possibilities, whatever is possible is or one day will be true.<ref name="kenny136"/> His pupil Philo, rejecting this, defined ''possible'' as "that which is capable of being true by the proposition's own nature",<ref name="ancientlogic"/> thus a statement like "this piece of wood can burn" is ''possible'', even if it spent its entire existence on the bottom of the ocean.<ref name="kenny138">{{Harvnb|Adamson|2015|p=138}}</ref> Chrysippus, on the other hand, was a causal determinist: he thought that true causes inevitably give rise to their effects and that all things arise in this way.<ref name="adamson58">{{Harvnb|Adamson|2015|p=58}}</ref> But he was not a logical determinist or fatalist: he wanted to distinguish between possible and necessary truths.<ref name="adamson58"/> Thus, he took a middle position between Diodorus and Philo, combining elements of both their modal systems.<ref name="bobzien120">{{Harvnb|Bobzien|1999|p=120}}</ref> Chrysippus's set of Stoic modal definitions was as follows:<ref name="bobzien118">{{Harvnb|Bobzien|1999|p=118}}</ref>
{| class="wikitable" style="margin:1.0em auto;"
! colspan="2" style="background:white;text-align:center;" | Modal definitions
|-
! Name
! Definition
|-
| style="white-space:nowrap;" | ''possible''
| style="white-space:wrap;" | An assertible which can become true '''and''' is not hindered by external things from becoming true
|-
| style="white-space:nowrap;" | ''impossible''
| style="white-space:wrap;" | An assertible which cannot become true '''or''' which can become true but is hindered by external things from becoming true
|-
| style="white-space:nowrap;" | ''necessary''
| style="white-space:wrap;" | An assertible which (when true) cannot become false '''or''' which can become false but is hindered by external things from becoming false
|-
| style="white-space:nowrap;" | ''non-necessary''
| style="white-space:wrap;" | An assertible which can become false '''and''' is not hindered by external things from becoming false
|}

=== Arguments ===
In Stoic logic, an argument is defined as a compound or system of premises and a conclusion.<ref name="bobzien121"> {{Harvnb|Bobzien|1999|p=121}}</ref> A typical Stoic [[syllogism]] is: "If it is day, it is light; It is day; Therefore it is light".<ref name="bobzien121"/> It has a non-simple assertible for the first premise ("If it is day, it is light") and a simple assertible for the second premise ("It is day").<ref name="bobzien121"/> Stoic logic also uses variables that stand for propositions to generalize arguments of the same form.<ref name="bobzien881">{{Harvnb|Bobzien|1996a|p=881}}</ref> In more general terms this argument would be:<ref name="sellars58"/> "If p, then q; p; Therefore q."

==== Indemonstrable arguments ====
Chrysippus listed five basic argument forms, called indemonstrables,<ref name="Mates">{{Harvnb|Mates|1953|pages=67–73 }}</ref>{{Ref label|C|c|none}} which all other arguments are reducible to:<ref name="ierodiakonou678">{{Harvnb|Ierodiakonou|2006|p=678}}</ref>
{| class="wikitable" style="margin:1.0em auto;"
! colspan="4" style="background:white;text-align:center;" | Indemonstrable arguments
|-
! Name{{Ref label|D|d|none}}
! Description
! Example
|-
|style="white-space:nowrap;"| [[Modus ponens]]
|style="white-space:nowrap;"| If p, then q.&nbsp; p.&nbsp; Therefore, q.
| ''If it is day, it is light. It is day. Therefore, it is light.''
|-
|style="white-space:nowrap;" | [[Modus tollens]]
|style="white-space:nowrap;"| If p, then q.&nbsp; Not q.&nbsp; Therefore, not p.
| ''If it is day, it is light. It is not light. Therefore, it is not day.''
|-
|style="white-space:nowrap;"| [[Modus ponendo tollens]]
|style="white-space:nowrap;"| Not both p and q.&nbsp; p.&nbsp; Therefore, not q.&nbsp;
| ''It is not both day and night. It is day. Therefore, it is not night.''&nbsp;
|-
|style="white-space:nowrap;"| [[Strong modus tollendo ponens]]
|style="white-space:nowrap;"| Either p or q.&nbsp; Not p.&nbsp; Therefore, q.
| ''It is either day or night. It is not day. Therefore, it is night.''
|-
|style="white-space:nowrap;"| [[Strong modus ponendo tollens]]
|style="white-space:nowrap;"| Either p or q.&nbsp; p.&nbsp; Therefore, not q.
| ''It is either day or night. It is day. Therefore, it is not night.''
|}

There can be many variations of these five indemonstrable arguments.<ref name="bobzien128">{{Harvnb|Bobzien|1999|p=128}}</ref> For example the assertibles in the premises can be more complex, and the following syllogism is a valid example of the second indemonstrable (''modus tollens''):<ref name="bobzien129"/> "if both p and q, then r; not r; therefore not: both p and q" Similarly one can incorporate negation into these arguments.<ref name="bobzien129"/> A valid example of the fourth indemonstrable (strong ''modus tollendo ponens'' or exclusive disjunctive syllogism) is:<ref name="shenefeltwhite87">{{Harvnb|Shenefelt|White|2013|p=87}}</ref> "either [not p] or q; not [not p]; therefore q" which, incorporating the principle of [[double negation]], is equivalent to:<ref name="shenefeltwhite87"/> "either [not p] or q; p; therefore q."

==== Complex arguments ====
However, many other arguments are not expressed in the form of the five indemonstrables, and the task is to show how they can be reduced to one of the five types.<ref name="sellars60"/> A simple example of Stoic reduction is reported by [[Sextus Empiricus]]:<ref name="ierodiakonou521">{{Harvnb|Ierodiakonou|2009|p=521}}</ref> "if both p and q, then r; not r; but also p; Therefore not q" This can be reduced to two separate indemonstrable arguments of the second and third type:<ref name="ierodiakonou522">{{Harvnb|Ierodiakonou|2009|p=522}}</ref> "if both p and q, then r; not r; therefore not: both p and q; not: both p and q; p; therefore not q"

The Stoics stated that complex syllogisms could be reduced to the indemonstrables through the use of four ground rules or ''themata''.<ref name="bobzien133">{{Harvnb|Bobzien|1996b|p=133}}</ref> Of these four ''themata'', only two have survived.<ref name="Kneale2">{{Harvnb|Kneale|Kneale|1962|p=169}}</ref><ref name="ancientlogic"/> One, the so-called first ''thema'', was a rule