The Stoics divided their philosophy into Logic, Ethics, and Physics.
Stoic logic included rhetoric, dialectic, grammar, epistemology and a philosophy of language. They developed theories of concepts, propositions, perception, and thought. Their logic was propositional, rather than the Aristotelian logic of syllogisms and predicates. They defined five fundamental logical tools:
if p then q; p; therefore q (modus ponens);
if p then q; not q; therefore not-p (modus tollens);
either p or q; p; therefore not-q;
either p or q; not p; therefore q;
not both p and q; p; therefore not-q;
They had a strict interpretation of the principle of bivalence (Aristotle's non-contradiction) and the law of the excluded middle. Every statement is either true or false, even statements about the future, as Diodorus Cronus
had denied the present truth or falsity of future statements with his analysis of future contingency
(e.g., the Sea Battle).
The Stoic philosophy of language had a theory of signs long before Charles Sanders Peirce
's semiotics or Ferdinand de Sausurre
's semiology. A signifier is an utterance of a name, a proper noun (onoma
). The name-bearer is the object or concept that gets signified. The signification consists of the immaterial qualities that they called lekta
, or ‘sayables,’ predicates that are true or false of the signified. The sayables are that which subsists (grows and decays) in an individual.
Stoic physics included a wide range of topics including ontology, cosmology, theology, psychology, and metaphysics. The basic principles of the universe (Aristotle's archai
) are two - matter and pneuma - an immaterial breath or psyche. Pneuma combined two of the four fundamental elements, fire and air, representing hot and cold, as the active principle. A passive principle combined earth and water as the basis for material objects. The Stoics regarded matter as "unqualified" and inert. Changes in the material in an object they described as generation and destruction (following Aristotle).
Pneuma is the cause (aition
) of change in the peculiar qualities of an individual that constitute growth and decay, corresponding to the Platonic and Aristotelian forms and ideas that shape
a material object. Pneuma endows the bodies with different qualities as a result. The pneuma of inanimate object is called a ‘tenor’ (hexis
, "having"). What it "has" are qualities. Pneuma in plants has a (phusis
, ‘nature’). Pneuma in animals the Stoics called soul (psychê
) and in rational animals pneuma includes the commanding faculty (hêgemonikon
The Stoics saw the identity
of an individual as its immaterial
bundle of properties or qualities that they called the "peculiarly qualified individual
" or ?δ?ο? ποι?ν.
Zeno of Cytium had formulated a psychological theory of how we acquire beliefs that are justified empirically and not by reasoning. To form a belief is to give one's assent to an "impression" (a phenomenal appearance: phantasia
) about the material substrate of an object. Some perceptions are ‘cognitive’ or self-warranting. Assenting to them is a cognition or grasp (katalêpsis
) of their objects. Assent should be restricted to these cognitive or kataleptic impressions. Cognitive impressions give us infallible knowledge or wisdom. Our beliefs will then be constituted entirely by self-warranting perceptual cognitions. Zeno argued that a cognitive impression "stamps" the form of the object (its peculiar qualities) on our mind or soul (pneuma
, the Stoics called the material substance or substrate ?ποκε?μενον (or "the underlying"). This material substrate is transformed when matter is lost or gained, but they said it is wrong to call such material changes "growth (α?ξ?σει?) and decay (φθ?σει?)." The Stoics suggested they should be called "generation (γεν?σει?) and destruction (φθορ??)." These terms were already present in Aristotle, who said that the form, the essence, is not generated. He said that generation and destruction are material changes that do not persist
(as does the Stoic peculiarly qualified individual).
It is therefore obvious that the form (or whatever we should call the shape in the sensible thing) is not generated—generation does not apply to it—nor is the essence generated; for this is that which is induced in something else either by art or by nature or by potency. But we do cause a bronze sphere to be, for we produce it from bronze and a sphere; we induce the form into this particular matter, and the result is a bronze sphere...
For if we consider the matter carefully, we should not even say without qualification that a statue is generated from wood, or a house from bricks; because that from which a thing is generated should not persist, but be changed. This, then, is why we speak in this way.
It is important to see that the Aristotelian view is very similar to the Stoic - that individuals are combinations of matter and form. At times Aristotle made the matter the principle of individuation
, at other times he stressed the immaterial
qualities or "affections," as did the Stoics, with their peculiarly qualified individual (?δ?ο? ποι?ν).
Is Aristotle here the source of the four Stoic genera or categories?
The term “substance” (ο?σ?α) is used, if not in more, at least in four principal cases; for both the essence and the universal and the genus are held to be the substance of the particular (?κ?στου), and fourthly the substrate (?ποκε?μενον). The substrate is that of which the rest are predicated, while it is not itself predicated of anything else. Hence we must first determine its nature, for the primary substrate (?ποκε?μενον) is considered to be in the truest sense substance.
Now in one sense we call the matter (?λη ) the substrate; in another, the shape (μορφ?); and in a third, the combination. Both matter and form and their combination are said to be substrate. of the two. By matter I mean, for instance, bronze; by shape, the arrangement of the form (τ? σχ?μα τ?? ?δ?α?); and by the combination of the two, the concrete thing: the statue (?νδρι??). Thus if the form is prior to the matter and more truly existent, by the same argument it will also be prior to the combination.
Aristotle clearly sees a statue
as an integral combination of its form/shape and its matter/clay, not two distinct things, as Skeptics would claim.
The Academic Skeptics
attacked the Stoics, saying Stoics were making single things into dual
beings, two objects in the same place at the same time, but indistinguishable.
. . . since the duality which they say belongs to each body is differentiated
in a way unrecognizable by sense-perception. For if a peculiarly qualified
thing like Plato is a body, and Plato's substance is a body, and there is no
apparent difference between these in shape, colour, size and appearance,
but both have equal weight and the same outline, by what definition and
mark shall we distinguish them and say that now we are apprehending
Plato himself, now the substance of Plato? For if there is some difference,
let it be stated and demonstrated
Many of the classic metaphysical puzzles are arguments over this dual nature of something as matter and form, especially
Dion and Theon
, Tibbles, the Cat
, The Growing Argument
, The Ship of Theseus
, and The Statue and the Clay
mistakenly think that matter alone constitutes