Hellenistic philosophy is Ancient Greek philosophy corresponding to the Hellenistic period in Ancient Greece, from the death of Alexander the Great in 323 BC to the Battle of Actium in 31 BC. The dominant schools of this period were the Stoics, the Epicureans and the Skeptics.

Background The preceding classical period in Ancient Greek philosophy had centered on Socrates (c. 470–399 BC), whose students Antisthenes, Aristippus, and Plato went on to found Cynicism, Cyrenaicism, and Platonism, respectively. Plato taught Aristotle who created the Peripatetic school and in turn had tutored Alexander the Great. Socrates' thought was therefore influential for many of these schools of the period, leading them to focus on ethics and how to reach eudaimonia.

Early Platonism, known as the "Old Academy," begins with Plato, followed by Speusippus (Plato's nephew), who succeeded him as the head of school (until 339 BC), and Xenocrates (until 313 BC). Both of them sought to fuse Pythagorean speculations on number with Plato's theory of forms. The Peripatetic school was composed of philosophers who maintained and developed the philosophy of Aristotle after his death, beginning with Theophrastus (371–287 BC) and Strato of Lampsacus (335–269 BC). They advocated examination of the world to understand the ultimate foundation of things. The goal of life was the eudaimonia which originated from virtuous actions, which consisted in keeping the mean between the two extremes of the too much and the too little.

The Hellenistic period began with the death of Alexander and Diogenes in 323 BC, followed by the death of Aristotle the next year in 322 BC. While the classical thinkers were mostly based in Athens, at end of the Hellenistic period philosophers relocated at Rome or Alexandria. The shift followed Rome's military victories from the middle of the second century BC. Sulla's capture of Athens in 87 BC led to destructions and the shipping of Aristotle's manuscripts to Rome. The end of the Hellenistic period does not correspond with anything philosophical, but gradually during the Roman imperial period the predominance of Ancient Roman philosophy becomes perceptible. According to A. C. Grayling, the greater insecurity and loss of autonomy of the era drove some to use philosophy as a means to seek inner security from the external world. This interest in using philosophy to improve life was captured in Epicurus' claim that "empty are the words of that philosopher who offers therapy for no human suffering".

Socratic schools Many of the Socratic schools continued to exert influence well into the Hellenistic period, including the Cynic, Cyrenaic and Megarian school.

Cynics Cynicism, as begun with Antisthenes, followed by Diogenes and Crates of Thebes, advocated purposefully living an ascetic life with only bare necessities in accordance with nature, rejecting all "unnatural pleasures" that were associated with society or its material benefits. Pleasures provided by nature (which would be immediately accessible) were acceptable, however. Crates hence claimed "Philosophy is a quart of beans and to care for nothing". Stoicism would be based on the ethical ideas of the Cynics.

Cyrenaics The Cyrenaics, beginning with Aristippus the Younger, the grandson of the founder, argued that the reason pleasure was good was that it was evident in human behavior from the youngest age, because this made it natural and therefore good (the so-called cradle argument). The Cyrenaics also believed that present pleasure freed one from anxiety of the future and regrets of the past, leaving one at peace of mind. These ideas were taken further by Anniceris (), who expanded pleasure to include things like friendship and honour. Theodorus (c. 340–250) disagreed with this and instead argued that social ties should be cut and self-sufficiency be espoused instead. Hegesias of Cyrene (fl. 290) on the other hand claimed that life could ultimately not be overall pleasurable.

Dialectical school The dialectical school was known for their study of paradoxes, dialectic, and propositional logic. The main philosophers associated with this school were Diodorus Cronus and Philo the Logician Besides studying logical puzzles and paradoxes, the Dialecticians made two important logical innovations, by re-examining modal logic, and by starting an important debate on the nature of conditional statements.* Through their development of propositional logic, the Dialectical school played an important role in the development of logic, which was an important precursor of Stoic logic.

Stoicism Stoicism was founded by Zeno of Citium in the third century BC, asserting that the goal of life was to live in accordance with nature. It advocated the development of self-control and fortitude as a means of overcoming destructive emotions. 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 Agora in Athens where Zeno and his followers gathered to discuss their ideas. Zeno's most influential follower was Chrysippus, who followed him as leader of the school after Cleanthes and was responsible for molding what is now called Stoicism. The Stoics provided a unified account of the world, constructed from ideals of logos, physics, and ethics.

Stoic logic

Chrysippus developed a system that became known as Stoic logic and included a deductive system, Stoic syllogistic, which was considered a rival to Aristotle's syllogistic. The Stoics held that all beings (ὄντα)—though not all things (τινά)—are material.Jacques Brunschwig, Stoic Metaphysics in The Cambridge Companion to Stoics, ed. B. Inwood, Cambridge, 2006, pp. 206–232 Besides the existing beings they admitted four incorporeals (asomata): time, place, void, and sayable.Sextus Empiricus, Adversus Mathematicos 10.218. (chronos, topos, kenon, lekton) They were held to be just 'subsisting' while such a status was denied to universals.Marcelo D. Boeri, The Stoics on Bodies and Incorporeals, The Review of Metaphysics, Vol. 54, No. 4 (Jun., 2001), pp. 723–752 Thus, they accepted Anaxagoras's idea (as did Aristotle) that if an object is hot, it is because some part of a universal heat body had entered the object. But unlike Aristotle, they extended the idea to cover all accidents. Thus, if an object is red, it would be because some part of a universal red body had entered the object.

The Stoics propounded that knowledge can be attained through the use of reason. Truth can be distinguished from fallacy—even if in practice only an approximation can be made. According to the Stoics, the senses constantly receive sensations: pulsations that pass from objects through the senses to the mind, where they leave an impression in the imagination (phantasiai) (an impression arising from the mind was called a phantasma). VII.49 The mind has the ability to judge (συγκατάθεσις, synkatathesis)—approve or reject—an impression, enabling it to distinguish a true representation of reality from one that is false. Some impressions can be assented to immediately, but others can achieve only varying degrees of hesitant approval, which can be labeled belief or opinion (doxa). It is only through reason that we gain clear comprehension and conviction (katalepsis). Certain and true knowledge (episteme), achievable by the Stoic sage, can be attained only by verifying the conviction with the expertise of one's peers and the collective judgment of humankind.

Stoic physics

According to the Stoics, the universe is a material reasoning substance (logos), which was divided into two classes: the active and the passive. The passive substance is matter, which "lies sluggish, a substance ready for any use, but sure to remain unemployed if no one sets it in motion".Seneca, Epistles, lxv. 2. The active substance is an intelligent aether or primordial fire, which acts on the passive matter. Everything is subject to the laws of fate, for the universe acts according to its own nature and the nature of the passive matter it governs. The souls of humans and animals are emanations from this primordial fire and are likewise subject to fate. Individual souls are perishable by nature and can be "transmuted and diffused, assuming a fiery nature by being received into the seminal reason ("logos spermatikos") of the universe".Marcus Aurelius, Meditations, iv. 21. Since right reason is the foundation of both humanity and the universe, it follows that the goal of life is to live according to reason, that is, to live a life according to nature. Similarly, space and the universe have neither start nor end, rather they are cyclical. The current universe is a phase in the present cycle, preceded by an infinite number of universes, doomed to be destroyed ("ekpyrōsis", conflagration) and re-created,Michael Lapidge, Stoic Cosmology, in: John M. Rist, The Stoics, Cambridge University Press, 1978, pp. 182–183. and to be followed by another infinite number of universes. Stoicism considers all existence as cyclical, the cosmos as eternally self-creating and self-destroying (see also eternal return).

Stoic passions

The foundation of Stoic ethics is that good lies in the state of the soul itself; in wisdom and self-control. One must therefore strive to be free of the passions. For the Stoics, reason meant using logic and understanding the processes of nature—the logos or universal reason, inherent in all things.   Present Future Good Delight Lust Evil Distress Fear For the Stoics, passions are evaluative judgements; a person experiencing such an emotion has incorrectly valued an indifferent thing. A fault of judgement, some false notion of good or evil, lies at the root of each passion. Incorrect judgement as to a present good gives rise to delight (hēdonē), while lust (epithumia) is a wrong estimate about the future. Unreal imaginings of evil cause distress (lupē) about the present, or fear (phobos) for the future. The ideal Stoic would instead measure things at their real value and see that the passions are not natural. To be free of the passions is to have a happiness which is self-contained. There would be nothing to fear—for unreason is the only evil; no cause for anger, for others cannot harm you.

The wise person (sophos) is someone who is free from the passions (apatheia). Instead the sage experiences good-feelings (eupatheia) which are clear-headed. These emotional impulses are not excessive but nor are they diminished emotions. Instead they are the correct rational emotions. The Stoics listed the good-feelings under the headings of joy (chara), wish (boulesis), and caution (eulabeia). Thus if something is present which is a genuine good, then the wise person experiences an uplift in the soul—joy (chara).

Epicureanism

Epicureanism was founded by Epicurus in the third century BC.

Atoms and void

Epicurean physics held that the entire universe consisted of two things: matter and void. Matter is made up of atoms, which are tiny bodies that have only the unchanging qualities of shape, size, and weight. The Epicureans believed that atoms were unchanging because the world was ordered and that changes had to have specific and consistent sources (e.g. a plant species only grows from a seed of the same species), but that in order for the universe to persist, what it is ultimately made up of must not be able to be changed or else the universe would be essentially destroyed.