[2.3] The Sceptic Mind according to Carneades

“The contribution for which Carneades (214-129/8 BC) is best known, however, came in response to the Stoics’ counter-argument in defense of the cognitive impression [2.2.1]. They contended that, without cognitive impressions, human beings would be deprived of any basis for action or inquiry. In reply Carneades argued that such a basis could be found in so-called probable impressions (from “probabilis,” that which lends itself to or invites approval, Cicero’s Latin for the Greek “pithanos,” persuasive).”

The following UML Use Case diagram shows the main concepts in the Sceptic epistemology:

The sceptic mind according to Carneades
FacultyRelated Use Case
PERCEPTIONExperience Impression (aisthetike phantasiai) through PERCEPTION
PERCEPTIONExperience Probable Impression (Pithanê phantasia): “though certainty is unobtainable, well founded  probabilities are within reach.” – Experience Non-Probable Impression
PERCEPTIONExperience Non-Probable Impression – if impression found IMPROBABLE
PERCEPTIONRational Action Initiation: “Rational action and inquiry are possible without… cognitive impressions… because probable impressions can serve in their place.”
REASON Investigation: “The account of probability explains how one can discriminate among impressions by investigating whether an initially persuasive impression agrees with one’s other impressions or if there is something about the conditions in which it arose that undermines confidence in it. The more such checks it survives, the more confidence one will have in it..
“…no amount of checking is sufficient to eliminate the possibility of error, it will be possible to achieve the degrees of confidence required in different circumstances to make rational action and theoretical inquiry possible”
REASON Form Well-founded Opinion: “…Carneades appeared to favor a more mitigated form of skepticism,  which admitted the possibility of well-founded opinions if not of certain knowledge”

The source of all citations and more about the topic in: Allen, James, “Carneades“, The Stanford Encyclopedia of Philosophy (Winter 2012 Edition), Edward N. Zalta (ed.)

First published: 02/02/2019


  • 06/02/2019: changed relationships of Investigation and Use Case names
  • 20/03/2019: changes relation of Rational Action Initiation

[2.2.5] Stoic Ontology, Genus, Categories

“An examination of Stoic ontology might profitably begin with a passage from Plato’s Sophist. There, Plato asks for a mark or indication of what is real or what has being. One answer which is mooted is that the capacity to act or be acted upon is the distinctive mark of real existence or ‘that which is.’ The Stoics accept this criterion and add the rider that only bodies can act or be acted upon. Thus, only bodies exist. So there is a sense in which the Stoics are materialists or – perhaps more accurately, given their understanding of matter as the passive principle (see below) – ‘corporealists’. However, they also hold that there are other ways of appearing in the complete inventory of the world than by virtue of existing. Incorporeal things like time, place or sayables (lekta, see below) are ‘subsistent’ – as are imaginary things like centaurs.”

In this diagram I used OntoUML notation to present the main concepts of Stoic ontology:

Cambridge: Cambridge University Press.
Comment texts from Stoic Ontology from Peter Wyss.
Something“This is the highest ontological genus: to be something (τί, ti) is to be some particular thing. Notably, this excludes Platonic Forms, or universals: they are not-somethings (outina), and thus ontological outcasts.” generalizes: Incorporeal; Body; Neither
Incorporeal“These do not exist, but subsist (ὑφεστάναι, hyphestanai); yet they are real (ὑπάρχειν, hyparchein). We can think of them as conditions ‘without which the interaction of bodies in the world would neither be analysable nor intelligible” generalizes: Sayable; Void; Place; Time
Place; Time; SayablePlace, time, sayabl are incorporeals.Place; Time; Sayable are subkidns of Incorporeal
Body“Only bodies (σώματα, sômata) have being, or exist. Slogan: to exist is to have causal powers. Plato in the Sophist (247d–e): ‘Now, I say that what has some power to make something else into something, or to suffer the slightest, even once, this has real being. For I define being as nothing but power (δύναμις).’ The Stoic conception of existence is thus dynamic. Matter as such is passive, but bodies are not, since they are also infused by logos, which is active… only bodies can act or be acted upon ”
Neither can be: fictional entities (e.g. unicorns); limitsgeneralizes: FictionalEntity; Limit
ObjectSubstrate“A dog as merely an object, something ‘out there’, a discrete portion of matter: a substance (οὐσία, ousia). As object, a dog is merely the potential bearer of qualities” component of Body; subkind of Body
DisposedA dog as a further differentiated qualified thing: as running, barking, brave. characterizes Body
Qualified“A dog as an object with certain qualities: bad breath, soft fur, dotted; can be qualified commonly as ‘dog’ or ‘furry’, or peculiarly as ‘Fido’.”associated with Body, one to zero or many multiplicity
RelativelyDisposed“A dog as an object in relation to other objects as owned by Jack, Rexs’ father winner at Crufts”mediates Body and Other Body
OtherBodythe reference body of relatively disposed, e.g. Jack; father role of Body


  • All citations from: Peter Wyss, “Stoic Ontology
  • Baltzly, Dirk, “Stoicism“, The Stanford Encyclopedia of Philosophy (Spring 2019 Edition), Edward N. Zalta (ed.)
  • Long, A. A. & Sedley, D. N. (1987). “The Hellenistic Philosophers”, Vol. 1 (p. 163). Cambridge: Cambridge University Press.

First published: 6/3/2019
Updated: 15/1/2022
Updated: 21/2/2022