As to the order in which the different departments should be studied, we have had preserved to us the actual words of Chrysippus in his fourth book on Lives. 'First of all then it seems to me that, as has been rightly said by the ancients, there are three heads under which the speculations of the philosopher fall, logic, ethic, physic; next, that of these the logical should come first, the ethical second, and the physical third, and that of the physical the treatment of the gods should come last, whence also they have given the name of "completions" to the instruction delivered on this subject'. That this order however might yield to convenience is plain from another book on the use of reason, where he says that 'the student who takes up logic first need not entirely abstain from the other branches of philosophy, but should study them also as occasion offers.'
Plutarch twits Chrysippus with inconsistency, because in the face of this declaration as to the order of treatment, he nevertheless says that morals rest upon physics. But to this charge it may fairly be replied that the order of exposition need not coincide with the order of existence. Metaphysically speaking, morals may depend upon physics and the right conduct of man be deducible from the structure of the universe but for all that, it may be advisable to study physics later. Physics meant the nature of God and the Universe. Our nature may be deducible from that but it is better known to ourselves to start with, so that it may be well to begin from the end of the stick that we have in our hands. But that Chrysippus did teach the logical dependence of morals on physics is plain from his own words. In his third book on the Gods he says 'for it is not possible to find any other origin of justice or mode of its generation save that from Zeus and the nature of the universe for anything we have to say about good and evil must needs derive its origin therefrom', and again in his Physical Theses, 'for there is no other or more appropriate way of approaching the subject of good and evil on the virtues or happiness than from the nature of all things and the administration of the universe—for it is to these we must attach the treatment of good and evil inasmuch as there is no better origin to which we can refer them and inasmuch as physical speculation is taken in solely with a view to the distinction between good and evil.'
The last words are worth noting as showing that even with Chrysippus who has been called the intellectual founder of Stoicism the whole stress of the philosophy of the Porch fell upon its moral teaching. It was a favourite metaphor with the school to compare philosophy to a fertile vineyard or orchard. Ethic was the good fruit, physic the tall plants, and logic the strong wall. The wall existed only to guard the trees, and the trees only to produce the fruit. Or again philosophy was likened to an egg of which ethic was the yolk containing the chick, physic the white which formed its nourishment while logic was the hard outside shell. Posidonius, a later member of the school, objected to the metaphor from the vineyard on the ground that the fruit and the trees and the wall were all separable whereas the parts of philosophy were inseparable. He preferred therefore to liken it to a living organism, logic being the bones and sinews, physic the flesh and blood, but ethic the soul.
LOGIC
The Stoics had a tremendous reputation for logic. In this department they were the successors or rather the supersessors of Aristotle. For after the death of Theophrastus the library of the Lyceum is said to have been buried underground at Scepsis until about a century before Christ, So that the Organon may actually have been lost to the world during that period. At all events under Strato the successor of Theophrastus who specialized in natural science the school had lost its comprehensiveness. Cicero even finds it consonant with dramatic propriety to make Cato charge the later Peripatetics with ignorance of logic! On the other hand Chrysippus became so famous for his logic as to create a general impression that if there were a logic among the gods it would be no other than the Chrysippean.
But if the Stoics were strong in logic they were weak in rhetoric. This strength and weakness were characteristic of the school at all periods. Cato is the only Roman Stoic to whom Cicero accords the praise of real eloquence. In the dying accents of the school as we hear them in Marcus Aurelius the imperial sage counts it a thing to be thankful for that he had learnt to abstain from rhetoric, poetic, and elegance of diction. The reader however cannot help wishing that he had taken some means to diminish the crabbedness of his style. If a lesson were wanted in the importance of sacrificing to the Graces it might be found in the fact that the early Stoic writers despite their logical subtlety have all perished and that their remains have to be sought for so largely in the pages of Cicero. In speaking of logic as one of the three departments of philosophy we must bear in mind that the term was one of much wider meaning than it is with us. It included rhetoric, poetic, and grammar as well as dialectic or logic proper, to say nothing of disquisitions on the senses and the intellect which we should now refer to psychology.
Logic as a whole being divided into rhetoric and dialectic: rhetoric was defined to be the knowledge of how to speak well in expository discourses and dialectic as the knowledge of how to argue rightly in matters of question and answer. Both rhetoric and dialectic were spoken of by the Stoics as virtues for they divided virtue in its most generic sense in the same way as they divided philosophy into physical, ethical, and logical. Rhetoric and dialectic were thus the two species of logical virtue. Zeno expressed their difference by comparing rhetoric to the palm and dialectic to the fist.
Instead of throwing in poetic and grammar with rhetoric, the Stoics subdivided dialectic into the part which dealt with the meaning and the part which dealt with the sound, or as Chrysippus phrased it, concerning significants and significates. Under the former came the treatment of the alphabet, of the parts of speech, of solecism, of barbarism, of poems, of amphibolies, of metre and music—a list which seems at first sight a little mixed, but in which we can recognise the general features of grammar, with its departments of phonology, accidence, and prosody. The treatment of solecism and barbarism in grammar corresponded to that of fallacies in logic. With regard to the alphabet it is worth noting that the Stoics recognised seven vowels and six mutes. This is more correct than our way of talking of nine mutes, since the aspirate consonants are plainly not mute. There were, according to the Stoics, five parts of speech—name, appellative, verb, conjunction, article. 'Name' meant a proper name, and 'appellative' a common term.
There were reckoned to be five virtues of speech—Hellenism, clearness, conciseness, propriety, distinction. By 'Hellenism' was meant speaking good Greek. 'Distinction' was defined to be 'a diction which avoided homeliness.' Over against these there were two comprehensive vices, barbarism and solecism, the one being an offence against accidence, the other against syntax.
The famous comparison of the infant mind to a blank sheet of paper, which we connect so closely with the name of Locke, really comes from the Stoics. The earliest characters inscribed upon it were the impressions of sense, which the Greeks called "phantasies." A phantasy was defined by Zeno as "an impression in the soul." Cleanthes was content to take this definition in its literal sense, and believe that the soul was impressed by external objects as wax by a signet ring. Chrysippus, however, found a difficulty here, and preferred to interpret the Master's saying to mean an alteration or change in the soul. He figured to himself the soul as receiving a modification from every external object which acts upon it just as the air receives countless strokes when many people are speaking at once. Further, he declared that in receiving an impression the soul was purely passive and that the phantasy revealed not only its own existence, but that also of its cause, just as light displays itself and the things that are in it. Thus, when through sight we receive an impression of white, an affection takes place in the soul, in virtue whereof we are able to say that there exists a white object affecting us. The power to name the object resides in the understanding. First must come the phantasy, and the understanding, having the power of utterance, expresses in speech the affection it receives from the object. The cause of the phantasy was called the "phantast," e. g. the white or cold object. If there is no external cause, then the supposed object of the impression was a "phantasm," such as a figure in a dream, or the Furies whom Orestes sees in his frenzy.