The Stoic Theory of Knowledge

The Stoics have answers to the questions (we saw in the last lecture) about knowledge and belief.

Cicero (106-43 BCE), Stanford Encyclopedia of Philosophy

Antiochus of Ascalon, Stanford Encyclopedia of Philosophy

Antiochus was not a Stoic, but he defended parts of Stoicism against the arguments of the Academics. Cicero spent time with Antiochus and discussed philosophy with him. So did Lucullus.

Lucullus (117-57 BCE) was a Roman general and statesman.
Lucullus' speech (II.11-62) in Cicero's Academica allows us to begin to see these answers. He speaks from the Stoic point of view. (Cicero's speech (II.64-147) in reply is from an Academic point of view.)

Lucullus' understanding of Stoicism comes from Antiochus.

"The arguments I’m going to make aren’t mine. ... I know the material, because I listened to [Antiochus] with my mind free and with considerable interest, and heard him quite often on the same subject" (Academica II.10).

Academica II.18

Philo is an Academic. Zeno is the founder of Stoicism.

Cicero's Latin translations of Greek philosophical terms can be hard to keep straight. Here is a partial list with English translations.

adsensio, "assent"
approbatio, "approval"
συγκατάθεσις, noun, "assent"

comprehensibilis, "graspable"
καταληπτός, adjective, "capable of being seized or grasped"

cognitio, "cognition"
comprehensio, "grasp"
perceptio, "taking in, receiving"
κατάληψις, noun, "seizing"

"...cognition (cognitio) or perception (perceptio) or, to translate literally, grasp (comprehensio), they call κατάληψις..." (Academica II.17).

φαντασία, noun, "impression"

visum comprehendible
καταληπτικὴ φαντασία, "cognitive impression"

inscientia, "ignorance"
ignorantia, "want of information, ignorance"
ἄγνοια, "want of perception, ignorance"

opinio, "opinion"
δόξα, "belief"

sapientia, "wisdom"

scientia, "knowledge"
ἐπιστήμη, "knowledge"

cognitus, adjective,
incognitus, adjective

notio, "concept or notion"
ἔννοια, noun,
πρόληψις, noun,

"By concept (notio) I mean what the Greeks call now ἔννοια, now πρόληψις. This is an innate knowledge of anything, which has been previously grasped, and needs to be unfolded" (Topica VII.1.31).

virtus, "virtue"
ἀρετή, "virtue"
When Philo claimed that nothing was graspable (this is how I translate ἀκατάληπτον) if it was as Zeno defined it— i.e., as an impression (by now we are used to this word for φαντασία) stamped and molded from its source in a way that it couldn’t be from what wasn’t its source. (In our view, Zeno’s definition was absolutely correct: how can you grasp anything, in such a way that you are quite confident that it is perceived or known, if something false could be just like it?)—Well, when Philo weakens and does away with this, he does away with the criterion of known and unknown. The result is that nothing is graspable—so he ends up unintentionally back in the position he was trying to avoid. For this reason, the purpose of my entire speech against the Academy is to retain the definition Philo wanted to overturn. And if I fail to attain that, I will concede that nothing can be perceived.

The Stoics think that animals and human beings have "impressions."

"An impression is an imprint on the soul" (Diogenes Laertius, Lives of the Philosophers VII.45) that represents what impressed itself on the soul. When, for example, someone says "I have the impression that the color of this webpage is white," he has an impression whose content is the proposition that the color of this webpage is white.

Impressions are not restricted to the sensory impressions. In adults, they arise in thinking too.

Because they have reason, impressions in adults are articulated in terms of concepts. The adult sees and thinks of things as things, a shade of white as a shade of white, a human being as a human being.

Animals and children lack reason. Their impressions somehow represent in terms of images.

Unlike animals and children, adults can "assent" to their impressions. it. Assenting to an impression results in belief or knowledge in the propositional content of the impression.

Varro, in his speech in Academica I, also says that Zeno talked about impressions.

"He considered sense-perceptions to be compounds of a kind of externally induced ‘impact’—he called this a φαντασίαν, but we can call it an ‘impression’ (and let’s hold on to this term, since we’re going to need it often in the rest of our conversation). But, as I was saying, he conjoined these—the impressions as received by the senses with the assent of our minds, which he took to be voluntary and have its source in us" (Academica I.40).

Among impressions, the Stoics distinguished what they called "cognitive impressions."

In Academica II.18, Lucullus talks about cognitive impressions indirectly. He talks about whether things are "graspable" or not. The Stoics think we grasp things when we have a cognitive impression of them.

Lucullus complaint about how Philo changed Zeno's definition is confusing.

The definition is of a cognitive impression. Lucullus says he will concede that "nothing can be perceived" if he fails to defend this definition. By "nothing can be perceived," he means that knowledge is impossible.

We will think more later about what this definition is and how Philo changed it.

The Latin percipi in "can be perceived (percipi)" is the present passive infinitive of percipio, which is a compound formed from per ("thoroughly") +‎ capio ("capture, seize"). This sense survives in English when someone is said to be "perceptive." Such a person grasps the facts ("sees" what is going on) in situations that often confuse others.

Academica II.19, II.20, II.21, II.22

Let’s start with the senses. ... In my judgment, there is a great deal of truth in the senses, providing they are healthy and properly functioning and all obstacles and impediments are removed. That’s why we often want the light changed or the positions of the things we’re looking at, and we reduce or increase their distance from us and alter many conditions until our vision itself provides the warrant for its own judgment. The same goes for sounds, smells, and flavours. So none of us would demand keener judgment in any of the various senses. (19)

But if you add the practice and skill that allow one’s eyes to dwell on paintings or one’s ears on songs, can anyone fail to see the power of the senses? There’s so much detail painters see in shadow and relief that we don’t see! And so much detail in music escapes us that practitioners in this field pick up on. (20)

"When a man is born, the Stoics say, he has the commanding-part of his soul like a sheet of paper ready for writing upon. On this he inscribes each of his conceptions. The first method of inscription is through the senses. For by perceiving something, e.g., white, they have a memory of it when it has departed. And when many memories of a similar kind have occurred, we then say we have experience. For the plurality of similar impressions is experience. Some conceptions arise naturally in the aforesaid ways and undesignatedly, others through our own instruction and attention. The later are called conceptions only, the former are called preconceptions as well. Reason, for which we are called rational, is said to be completed from our preconceptions during our first seven years" (Pseudo-Plutarch, Placita 4.11).

Pseudo-Plutarch (2nd century CE) Placita Philosophorum (Views of the Philosophers) (once wrongly attributed to Plutarch) sets out five books of views of the philosophers on physics. Stobaeus (5th century CE) and Theodoret (5th century CE) preserve parts of this same work. Theodoret names (the otherwise unknown) Aëtius as the source.

The tradition of works of the views of the philosophers begins with Theophrastus, Aristotle's successor in the Lyceum. Diogenes Laertius lists "sixteen books of Physical Opinions" in the catalog of works he attributes to Theophrastus (Lives of the Philosophers V.2.48).
[Next we grasp thing such as] ‘That is white’, ‘This is sweet’, ‘That is melodious’, ‘This is fine-scented’, ‘This is rough’. This comes from the mind rather than the senses. Next comes: ‘That is a horse’, ‘That is a dog’. Then ... ‘If something is human, it is a mortal animal partaking in reason.’ It’s from this set that our conceptions of things are stamped on our minds, and without them there can be no understanding, investigation, or argument. (21)

"But suppose there were false conceptions (I understood you to use notitias for ἐννοίας). If our conceptions were false or stamped on our minds from impressions that couldn’t be discriminated from false impressions, then how would we put them to use? How would we see what was compatible with something or incompatible with it? (22)

The Stoics thinks we are not born with reason. We develop it as we become adults.

They also think that certain "conceptions" are essential to reason. This is a little confusing, but the idea seems to be that when we have these conceptions of things, we know certain necessary truths about how the world is. Lucullus gives an example: "if something is human, then it is a mortal animal partaking of reason."

Experience enables us to have these truths, but we do not infer these truths from our experience. Instead, because of what human beings are, we get these truths as part of what happens as we mature from children into adults.

Why do human beings get conceptions that give them truths as opposed to falsehoods?

Nature in its providence ensures this. It constructs us so that in the process of becoming adults, our experience transforms us so that we get reason and the conceptions that give us certain truths about how the world is.

Lucullus thinks that this would not happen if there were no cognitive impressions.

Academica II.23

"They say there is knowledge and opinion and, set midway between these two, cognition; and of these knowledge is the unerring and firm cognition which is unalterable by reason, and opinion is weak and false assent, and grasp is intermediate between these, being assent to a cognitive impression; and a cognitive impression, according to them, is one which is true and of such a kind as to be incapable of becoming false. And they say that knowledge is only in the wise, and opinion only in the fools, but cognition is shared alike by both, and it is the criterion of truth" (Sextus Empricius, Against the Logicians I.151).

"These men, then, assert that the criterion of truth is the cognitive impression" (Sextus Empiricus, Against the Logicians I.227).

"[A cognitive impression] being plainly evident and striking, lays hold of us, almost by the very hair, as they say, and drags us off to assent, needing nothing else to help it to be thus impressive or to suggest its superiority over all others. For this reason, too, every man, when he is anxious to cognize any object exactly, appears of himself to pursue after an impression of this kind—as, for instance, in the case of visible things, when he receives a dim impression of the real object. For he intensifies his gaze and draws close to the object of sight so as not to go wholly astray, and rubs his eyes and in general uses every means until he can receive a clear and striking impression of the thing under inspection" (Sextus Empiricus, Against the Logicians I.257).

"[A]ccording to the Stoics the cognitive impression is judged to be cognitive by the fact that it proceeds from an existing object and in such a way as to bear the impress and stamp of that existing object; and the existing object is approved as existent because of its exciting a cognitive impression" (Sextus Empiricus, Against the Ethicists 183).
The study of the virtues also provides very strong confirmation that many things are perceived and grasped. We define knowledge as not just a grasp of something, but one that is secure and immutable. Likewise for wisdom, the art of life, which gives rise to the constancy of the wise. If their constancy didn’t depend on any grasp or knowledge, I’d like to know how it comes to be and why the good man resolves to endure every torture or be wracked by intolerable pain rather than give up on an appropriate action or his word. Why would he impose such heavy constraints as these on himself if he didn’t rely on anything grasped, perceived or known that would explain why this was fitting? It’s impossible for anyone to value impartiality and fidelity so highly that there’s no punishment he would refuse in order to maintain them, unless he has given his assent to that can’t be false. (23)

Lucullus gives the Stoic definition of knowledge. It is a "grasp ... that is secure and immutable."

A grasp consists in an assent to a cognitive impression. (The Stoics use κατάληψις for this grasp.) We can describe the act of assenting to a cognitive impression as "cognizing" and of the result as a "cognition."

The Stoics think of cognition as between opinion and knowledge. Opinions are true and false and are not secure. Cognitions are always true but not secure. Knowledge is both true and secure.

What does "secure and immutable" mean here?

Varro, in his speech in Academica I, helps us see the meaning.

“Zeno didn’t put his trust in all impressions but only in those that revealed their objects in a special way. Since this kind of impression could be discerned just by itself, he called it graspable —Can you bear this?
  Of course, Atticus replied, how else could you translate καταληπτόν?
  But once it had been received and approved, he called it a grasp, like something grasped by one’s hand. (In fact, that was his source for this term, since no one had used this word for that kind of thing before. Zeno used a lot of novel terms, but what he was saying was new, too.) ... And if it had been grasped in such a way that it couldn’t be dislodged by reason, he called it knowledge, if not, ignorance. The latter was also the source of opinion, which was a weak condition covering false as well as unknown" (Academica I.41).

Reason cannot convince someone with knowledge to withdraw his assent.

Socrates' interlocutors did not have knowledge. They thought they did, but he convinced them in dialectic that their own beliefs committed them to the negation of what they asserted.

The Stoics do not think that someone might have knowledge about some things but only opinions about others. They think that only the wise have knowledge and that the wise have no opinions.

This explains why they think someone with knowledge is not subject to refutation in dialectic.

                                         Q    R    S
                        P                   not-P

In the case of the wise, because they have no false beliefs, the conditions for refutation in dialectic cannot be met.

We, it seems, do not think of the wise as the Stoics did. Someone who is wise would know what to do in situations that would confuse many of us, but we do not require them to have no false beliefs.

We do not think of knowledge as the Stoics did either. For them, knowledge is exceedingly rare cognitive state. It is present only in the wise, and they think that either no one or almost no one is wise.

Academica II.24

appetitio, "a grasping at, reaching after"
ὁρμή, noun, "impulse"

"impulsive impressions" (φαντασίαι ὁρμητικαί)
Here’s another obvious point: something must be determined as the initial thing for wisdom to follow when it begins to act, and that initial thing must be suited to our nature. Otherwise our impulse (I mean this to translate ὁρμήν)— which stirs us to action, i.e., to have an impulse towards the object of our impression—can’t be moved. But we must first have an impression of what moves our impulse, and believe it, and that can’t happen if the object of our impression can’t be discriminated from something false. So how can the mind be moved to have an impulse if it doesn’t perceive whether the object of the impression is suited to our nature or alien to it? (24)

The Stoics understand behavior in terms of "impulsive impressions."

The evidence for how this works is limited.

Here is a possibility.

Impressions are impulsive against the background of our beliefs about what is good and what is bad.

The Stoic understanding of the good life is not what we might expect.

They believe that only wisdom is good. The Stoic sage is not confused about this. His beliefs about what is good and what is bad are true.

The Stoic sage thinks too that nature in its providence has arranged things so that things happen in the world with the utmost wisdom. The sage, though, is not omniscient. So he does not always know what will happen. He knows that in general living things find food when they are hungry, recover from illness when they are ill, and so on. So, for example, when he gets sick, he takes steps to recover. His impulses, though, are not excessive because he knows that his recovering or not is neither good nor bad. If it becomes clear to him that he is not going to recover, he is not upset. He knows that wisdom is the only good, and he now understands that in his particular case the wisdom with which nature arranges things does not include him recovering from his illness.

The Stoic sage, in living this way, experiences a joy the rest of us cannot match. We have false beliefs about what is good and what is bad. We think, for example, that illness and death are bad. So when this or other things we regard as bad happens to us or our loved ones, we are upset.
This is most straightforward to understand when these beliefs are false from the Stoic point of view. The belief that death is bad is an example. Suppose I believe this and in particular that my death is bad, and suppose that I get the impression that I might die (because, say, I inadvertently ate some poisoned food). This impression is alarming and deeply disturbing to me, and if I were assent to it (and thus form the belief that I might die), I would have what the Stoics call an "excessive impulse" (ὁρμὴ πλεονάζουσα) to do what I can to prevent my death.

Suppose, alternatively, that I have what the Stoics think are true beliefs about what is good and what is bad.

I understand, then, that nature in its providence arranges things so that in general living things find food when they are hungry, recover from illness when they are ill, and so on. I am not omniscient. So I do not know whether nature has arranged things so that in my particular case the cut will heal and I will not die, but given my understanding of the arrangement in nature generally, I know that it is reasonable for me to try to avoid my death. I am concerned, then, to take steps to avoid my death, but my impulse is not excessive.

It can be tempting to think the reasoning here has the following form:

1. Nature has generally arranged things so that P’s are Q’s.
2. I am a P.
3. Nature has arranged things so that I am a Q.

Note, though, that in this reasoning I believe something I may come to think is false if I get new information that convinces me that my death is part of how nature in its providence arranges things. I might notice that the poison is making me feel numb and this numbness is spreading rapidly. I am not upset if this happens because I don't have false beliefs about what is good and what is bad. I do not think my death is bad.

The wise, though, according to the Stoics, do not have false beliefs.

So how do the wise reason?

Maybe there is an answer in the following story Diogenes Laertius reports:

"Sphaerus [a Stoic] went to Ptolemy Philopator at Alexander. One day there was a discussion about whether a wise man would allow himself to be guided by opinion, and when Sphaerus affirmed that he would not, the king, wishing to refute him, ordered some pomegranates of wax to be set before him; and when Sphaerus was deceived by them, the king shouted that he had given his assent to a false impression. But Sphaerus answered very neatly, that he had not given his assent to the fact that they were pomegranates, but to the fact that it was reasonable (εὔλογόν) that they are pomegranates. And he pointed out that a cognitive impression and a reasonable impression are different" (Diogenes Laertius, Lives of the Philosophers VII.177).

What is the view here?

The "reasonable impression" seems to be the impression that it is reasonable that these things I see are pomegranates.

This impression is not opinion. So it must be knowledge.

Is this impression cognitive?

The text can suggest it is not, but it must be cognitive if the assent is knowledge.

So maybe the point Sphaerus makes is that although not every impression with the propositional content that it is reasonable that these things I see are pomegranates is cognitive, the one to which he assented was cognitive.

Academica II.77

None of Zeno’s predecessors had ever explicitly formulated, or even suggested, that no one should hold opinions—and not just that they could, but that doing so was necessary for the wise man. Arcesilaus thought that this view was both true and honourable, as well as right for the wise man. So he asked Zeno, we may suppose, what would happen if the wise person couldn’t perceive anything, but it was a mark of wisdom not to hold opinions. Zeno replied, no doubt, that the wise person wouldn’t hold any opinions because there was something that could be perceived. What was that? An impression, I suppose. What kind of impression? Zeno defined it thus: an impression from what is, stamped, impressed, and molded just as it is. Arcesilaus went on to ask what would happen if a true impression was just like a false one. At this point, Zeno was sharp enough to see that no impression could be perceived if one that came from what is was such that there could be one just like it from what is not. Arcesilaus agreed that this was a good addition to the definition, since neither a false impression, nor a true impression just like a false one, could be perceived. So then he set to work with his arguments, to show that there is no impression from something true such that there could not be one just like it from something false. (77)

Cicero is the speaker.

"Since all things are non-graspable owing to the nonexistence of the Stoic criterion, the wise man will opine if he assents; for when nothing is graspable, if he assents to anything he will be assenting to what is not graspable, and assent to this is opinion. So that if the wise man is among the assenters, he is among those who opine. But the wise man, to be sure, is not among those who opine (for, according to them [the Stoics], opinion is a mark of folly and a cause of error); therefore the wise man is not among assenters. And if this be so, he will necessarily refuse assent in all cases. But to refuse assent is nothing else than to suspend judgement; therefore the wise man will in all cases suspend judgement" (Sextus Empiricus, Against the Logicians (M.VII) I.156). The Stoic view is surprising. They think that holding opinions is irrational.

Cicero says that Arcesilaus thought this Stoic view is true. We may doubt this. Arcesilaus is engaging in dialectic.

The dialectic itself looks pretty unrealistic.

The important point is the Stoics commit themselves to the existence of cognitive impressions.

Zeno's definition of these impressions is confusing to think about.

A cognitive impression, first of all, is "from what is, stamped, impressed, and molded just as it is."

This means, it seems, that the propositional content of the impression is true.

Suppose I get an impression that Socrates is approaching and that in fact Socrates is approaching. His approaching stamps and impresses itself on me as my impression that Socrates is approaching.

If, alternatively, I get an impression that Socrates is approaching but in fact the person approaching is not Socrates but someone I mistook for him, then what give me my impression is not his approaching.

A cognitive impression, then, is true. This is the first part of the definition.

The second part is that a cognitive impression is "such that there could [not] be one just like it from what is not."

This second part of the definition of a cognitive impression is harder to understand than the first.

Suppose that when I get an impression that Socrates is approaching, the light is not good and he is pretty far away. The impression is true. He is approaching, but it seems that I easily might have been wrong.

So there are two cases. The first is the actual case. In it, I have a true impression that Socrates is approaching. The second case is what could have happened. In it, I have a false impression that Socrates is approaching. There are, then, two impressions (one actual, one possible) with the same propositional content (that Socrates is approaching). If the possible impression is "just like" the actual impression, the actual impression is true but not cognitive.

What does "just like" mean here?

We will think about this more when we look the Academic arguments "to show that there is no impression from something true such that there could not be one just like it from something false."

Academica II.145

Yes, but you deny that anyone knows anything, except the wise. Zeno used to demonstrate this with gestures. When he had put his hand out flat in front him with his fingers straight, he would say that an impression is like this. Next, after contracting his fingers a bit, he would say that assent is like this. Then, when he had bunched his hand up to make a fist, he would say that that was a grasp. (This image also suggested the name he gave to it, κατάληψιν, which hadn’t been used before.) "It oftener happens that a mule brings forth a colt than that nature produces a wise man" (Cicero, On Divination II.28.61).

"According to [the Stoics], ... of men the greatest number are bad, or rather there are one or two whom they speak of as having become good men as in a fable, a sort of incredible creature as it were and contrary to nature and rarer than the Ethiopian phoenix; and the others are all wicked and are so to an equal extent, so that there is no difference between one and another, and all who are not wise are alike mad" (Alexander of Aprodisias, De fato XXVIII).

For the Ethiopian phoenix, see Herodotus, Histories II.73.1 and Pliny the Elder, The Natural History X.2.
Finally, when he had put his left hand on top, squeezing his fist tight with some force, he would say that knowledge was like that: a state none but the wise enjoyed—though as for who is or ever was wise, even they aren’t in a rush to say. (145)

Cicero is the speaker here.

The Stoics think that we have impressions. If the impression is cognitive, assent to it results in a grasp or cognition. Knowledge is cognition that no rational means can force one to withdraw his assent.

Only the wise have knowledge.

The wise are extremely rare. Most of us are fools.

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