Pyrrhonism in the context of "Phenomena"

Academic skepticism was the philosophy of the skeptical period of the Academy dating from around 266 BCE, when Arcesilaus became scholarch, until around 90 BCE, when Antiochus of Ascalon rejected skepticism, although individual philosophers, such as Favorinus and his teacher Plutarch, continued to defend skepticism after this date. Unlike the existing school of skepticism, the Pyrrhonists, they maintained that knowledge of things is impossible. Ideas or notions are never true; nevertheless, there are degrees of plausibility, and hence degrees of belief, which allow one to act. The school was characterized by its attacks on the Stoics, particularly their dogma that convincing impressions led to true knowledge. The most important Academics were Arcesilaus, Carneades, and Philo of Larissa. The most extensive ancient source of information about Academic skepticism is Academica, written by the Academic skeptic philosopher Cicero.

A phenomenon (pl. phenomena), sometimes spelled phaenomenon, is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which cannot be directly observed. Kant was heavily influenced by Gottfried Wilhelm Leibniz in this part of his philosophy, in which phenomenon and noumenon serve as interrelated technical terms. Far predating this, the ancient Greek Pyrrhonist philosopher Sextus Empiricus also used phenomenon and noumenon as interrelated technical terms.

Acatalepsy (from the Greek α̉- 'privative' and καταλαμβάνειν 'to seize'), in philosophy, is incomprehensibleness, or the impossibility of comprehending or conceiving some or all things. The doctrine held by the ancient Skeptic philosophers, that human knowledge never amounts to certainty, but only to probability.

The Pyrrhonians attempted to show, while Academic skeptics of the Platonic Academy asserted an absolute acatalepsia; all human science or knowledge, according to them, went no further than to appearances and verisimilitude. It is the antithesis of the Stoic doctrine of katalepsis or Apprehension. According to the Stoics, katalepsis was true perception, but to the Skeptics, all perceptions were acataleptic, i.e. bear no conformity to the objects perceived, or, if they did bear any conformity, it could never be known.

Sextus Empiricus (Ancient Greek: Σέξτος Ἐμπειρικός, Sextos Empeirikos; fl. mid-late 2nd century CE) was a Greek Pyrrhonist philosopher and Empiric school physician with Roman citizenship. His philosophical works are the most complete surviving account of ancient Greek and Roman Pyrrhonism, and because of the arguments they contain against the other Hellenistic philosophies, they are also a major source of information about those philosophies.

In Ancient Greek philosophy, ataraxia (Greek: ἀταραξία, from ἀ- indicating negation or absence and ταρασσ- tarass- 'to disturb, trouble' with the abstract noun suffix -ία), generally translated as 'unperturbedness', 'imperturbability', 'equanimity', or 'tranquility', is a lucid state of robust equanimity characterized by ongoing freedom from distress and worry. In non-philosophical usage, ataraxia was the ideal mental state for soldiers entering battle. Achieving ataraxia is a common goal for Pyrrhonism, Epicureanism, and Stoicism, but the role and value of ataraxia within each philosophy varies in accordance with their philosophical theories. The mental disturbances that prevent one from achieving ataraxia also vary among the philosophies, and each philosophy has a different understanding as to how to achieve ataraxia.